Australian security services have disrupted a plot to blow up an aeroplane, Prime Minister Malcolm Turnbull has announced.
Police arrested four people in connection with the alleged plan.
Counter-terrorism raids took place took place in Sydney on Saturday afternoon.
Mr Turnbull said they were "designed to disrupt and prevent plans to undertake terrorist attacks in Australia".
It is not known what the specifics were or when the attack was scheduled to take place, but is believed an Improvised Explosive Device (IED) was the intended weapon.
The operation was carried out by the Australian Federal Police, the New South Wales state police and the Australian Security Intelligence Organisation, the country's domestic spy agency.
"Four men have been taken into custody and are assisting police with their enquiries," a police statement said.
Seven Network television reported that 40 riot squad officers stormed an inner-Sydney house before an explosives team found a suspicious device.
Mr Turnbull said he was briefed on the progress of the operation by security agency chiefs.
"My number one priority, and that of my government, is the safety and security of all Australians, and the public should be reassured that our security and intelligence agencies are working tirelessly to keep us safe," the prime minister said in a statement.
Security at airports across the country has been increased after the operation, the Sydney Morning Herald reported. Mr Turnbull advised travellers to get to airports earlier than usual.
29 July 2017
Cyclists at the start of the first stage of the Tour de Pologne cycling race, over 130km from Krakow's Main Market Square, Poland
EPA28 July 2017
Israeli border guards keep watch as Palestinian Muslim worshippers pray outside Jerusalem's old city overlooking the Al-Aqsa mosque compound
Ahmad Gharabli/AFP28 July 2017
A supporter of Pakistan's Prime Minister Nawaz Sharif passes out after the Supreme Court's decision to disqualify Sharif in Lahore
Reuters/Mohsin Raza27 July 2017
Australian police officers participate in a training scenario called an 'Armed Offender/Emergency Exercise' held at an international passenger terminal located on Sydney Harbour
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27 July 2017
North Korean soldiers watch the south side as the United Nations Command officials visit after a commemorative ceremony for the 64th anniversary of the Korean armistice at the truce village of Panmunjom in the Demilitarized Zone (DMZ) dividing the two Koreas
Reuters/Jung Yeon-Je26 July 2017
Bangladeshi commuters use a rickshaw to cross a flooded street amid heavy rainfall in Dhaka. Bangladesh is experiencing downpours following a depression forming in the Bay of Bengal.
Munir Uz Zaman/AFP26 July 2017
The Soyuz MS-05 spacecraft for the next International Space Station (ISS) crew of Paolo Nespoli of Italy, Sergey Ryazanskiy of Russia, and Randy Bresnik of the U.S., is transported from an assembling hangar to the launchpad ahead of its upcoming launch, at the Baikonur Cosmodrome in Baikonur, Kazakhstan
Reuters/Shamil Zhumatov25 July 2017
A protester shouts at U.S. President Donald Trump as he is removed from his rally with supporters in an arena in Youngstown, Ohio
Reuters23 July 2017
Indian supporters of Gorkhaland chant slogans tied with chains during a protest march in capital New Delhi. Eastern India's hill resort of Darjeeling has been rattled at the height of tourist season after violent clashes broke out between police and hundreds of protesters of the Gorkha Janmukti Morcha (GJM) – a long-simmering separatist movement that has long called for a separate state for ethnic Gorkhas in West Bengal. The GJM wants a new, separate state of "Gorkhaland" carved out of eastern West Bengal state, of which Darjeeling is a part.
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23 July 2017
Demonstrators clash with riot security forces while rallying against Venezuela's President Nicolas Maduro's government in Caracas, Venezuela. The banner on the bridge reads "It will be worth it"
Reuters22 July 2017
The Heathcote river as it rises to high levels in Christchurch, New Zealand. Heavy rain across the South Island in the last 24 hours has caused widespread damage and flooding with Dunedin, Waitaki, Timaru and the wider Otago region declaring a state of emergency.
Getty Images22 July 2017
A mourner prays at a memorial during an event to commemorate the first anniversary of the shooting spree that one year ago left ten people dead, including the shooter in Munich, Germany. One year ago 18-year-old student David S. shot nine people dead and injured four others at and near a McDonalds restaurant and the Olympia Einkaufszentrum shopping center. After a city-wide manhunt that caused mass panic and injuries David S. shot himself in a park. According to police David S., who had dual German and Iranian citizenship, had a history of mental troubles.
Getty21 July 2017
Palestinians react following tear gas that was shot by Israeli forces after Friday prayer on a street outside Jerusalem's Old City
Reuters/Ammar Awad21 July 2017
Ousted former Thai prime minister Yingluck Shinawatra greets supporters as she arrives at the Supreme Court in Bangkok, Thailand
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20 July 2017
Marek Suski of Law and Justice (PiS) (C) party scuffles with Miroslaw Suchon (2nd L) of Modern party (.Nowoczesna) as Michal Szczerba of Civic Platform (PO) (L) party holds up a copy of the Polish Constitution during the parliamentary Commission on Justice and Human Rights voting on the opposition's amendments to the bill that calls for an overhaul of the Supreme Court in Warsaw
Reuters20 July 2017
A firefighter stands near a grass fire as he prepares to defend a home from the Detwiler fire in Mariposa, California
Reuters19 July 2017
Michael Lindell ,CEO of My Pillow reacts as U.S. President Donald Trump attends a Made in America roundtable meeting in the East Room of the White House
Reuters18 July 2017
Giant pandas lie beside ice blocks at Yangjiaping Zoo in Chongqing, China. Yangjiaping Zoo provided huge ice blocks for giant pandas to help them remove summer heat
Getty Images18 July 2017
People ride camels in the desert in Dunhuang, China, as stage 10 of The Silkway Rally continues
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18 July 2017
17th FINA World Aquatics Championships in Budapest, Hungary. Team North Korea practice under coach supervision
REUTERS17 July 2017
IAAF World ParaAthletics Championships - London, Britain - July 17, 2017
Reuters/Henry Browne17 July 2017
Workers check power lines during maintenance work in Laian, in China's eastern Anhui province
AFP/Getty Images17 July 2017
Russia Kamaz's driver Dmitry Sotnikov, co-drivers Ruslan Akhmadeev and Ilnur Mustafin compete during the Stage 9 of the Silk Way 2017 between Urumqi and Hami, China
Franck Fife/AFP/Getty Images17 July 2017
Australian Prime Minister Malcolm Turnbull talks with Special Operations Command soldiers during a visit to the Australian Army's Holsworthy Barracks in western Sydney
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16 July 2017
Men in traditional sailor costumes celebrate after carrying a statue of the El Carmen Virgin, who is worshipped as the patron saint of sailors, into the Mediterranean Sea during a procession in Torremolinos, near Malaga, Spain
Reuters/Jon Nazca16 July 2017
People participate in a protest in front of the Sejm building (the lower house of the Polish parliament) in Warsaw, Poland. The demonstration was organized by Committee for the Defense of Democracy (KOD). Members and supporters of the KOD and opposition parties protested against changes in the judicial law and the Supreme Court
EPA16 July 2017
People prepare to swim with a portrait of late Chinese Chairman Mao Zedong on the bank of the Yangtze River in Yichang, Hubei province, China to celebrate the 51st anniversary of Chairman Mao swimming in the Yangtze River.
REUTERS15 July 2017
A woman takes a selfie picture with her mobile phone next to the statue of Omer Halisdemir in Istanbul, in front of a memorial with the names of people killed last year during the failed coup attempt .
AFP/Getty Images14 July 2017
French President Emmanuel Macron gestures next to US President Donald Trump during the annual Bastille Day military parade on the Champs-Elysees avenue in Paris.
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13 July 2017
Philippine National Police chief Ronald Bato Dela Rosa holds an M60 machine gun during a Gun and Ammunition show at a mall in Mandaluyong city, metro Manila, Philippines
Reuters13 July 2017
Ukrainian President Petro Poroshenko and European Commission President Jean-Claude Juncker embrace before the EU-Ukraine summit in Kiev, Ukraine
Reuters13 July 2017
US President Donald Trump (R) and First Lady Melania Trump disembark form Air Force One upon arrival at Paris Orly airport on July 13, 2017, beginning a 24-hour trip that coincides with France's national day and the 100th anniversary of US involvement in World War I
Saul Loeb/AFP/Getty Images12 July 2017
Iraqis walk on a damaged street in west Mosul a few days after the government's announcement of the liberation of the embattled city from Islamic State (IS) group fighters
Getty12 July 2017
Iraqi boys wash a vehicle in west Mosul a few days after the government's announcement of the liberation of the embattled city from Islamic State (IS) group fighters
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11 July 2017
Afghan policeman pour fuel over jerry cans containing confiscated acetic acid before setting it alight on the outskirts of Herat. Some 15,000 liters of acetic acid, often mixed with heroin, were destroyed by counter narcotics police
Hoshang Hashimi/AFP11 July 2017
Residents stand amid the debris of their homes which were torn down in the evicted area of the Bukit Duri neighbourhood located on the Ciliwung river banks in Jakarta
Bay Ismoyo/AFP11 July 2017
Boys play cricket at a parking lot as it rains in Chandigarh, India
Reuters/Ajay Verma10 July 2017
Turkey's President Recep Tayyip Erdogan speaks at the 22nd World Petroleum Congress (WPC) in Istanbul
AFP10 July 2017
Police from the anti-terror squad participate in an anti-terror performance among Acehnese dancers during a ceremony to commemorate the 71st anniversary of the Indonesian police corps in Banda Aceh
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10 July 2017
New Mongolia's president Khaltmaa Battulga takes an oath during his inauguration ceremony in Ulaanbaatar, Mongolia
Reuters10 July 2017
US army 1st Division, US air force, US Navy and US Marines, march down the Champs Elysees, with the Arc de Triomphe in the background, in Paris during a rehearsal of the annual Bastille Day military parade
AFP9 July 2017
Participants run ahead of Puerto de San Lorenzo's fighting bulls during the third bull run of the San Fermin festival in Pamplona, northern Spain. Each day at 8:00 am hundreds of people race with six bulls, charging along a winding, 848.6-metre (more than half a mile) course through narrow streets to the city's bull ring, where the animals are killed in a bullfight or corrida, during this festival, immortalised in Ernest Hemingway's 1926 novel "The Sun Also Rises" and dating back to medieval times and also featuring religious processions, folk dancing, concerts and round-the-clock drinking.
AFP/Getty Images8 July 2017
Iraqi women, who fled the fighting between government forces and Islamic State (IS) group jihadists in the Old City of Mosul, cry as they stand in the city's western industrial district awaiting to be relocated
AFP8 July 2017
US President Donald Trump arrives for another working session during the G20 summit in Hamburg, northern Germany
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7 July 2017
People climb up on a roof to get a view during riots in Hamburg, northern Germany, where leaders of the world's top economies gather for a G20 summit
AFP/Getty Images7 July 2017
A military helicopter rescues people trapped on the roof of the Ministry of Finance by an intense fire in San Salvador
AFP/Getty Images6 July 2017
Donald Trump arrives to deliver a speech at Krasinski Square in Warsaw, Poland.
AP6 July 2017
A firefighter conducts rescue operations in an area damaged by heavy rain in Asakura, Japan.
Reuters6 July 2017
Anti-capitalism activists protest in Hamburg, where leaders of the world’s top economies will gather for a G20 summit.
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6 July 2017
Crowds gather for the start of the San Fermin festival in Pamplona, Spain.
AFP5 July 2017
A member of the Iraqi security forces runs with his weapon during a fight between Iraqi forces and Islamic State militants in the Old City of Mosul, Iraq.
5 July 2017
A U.S. MGM-140 Army Tactical Missile is fired during the combined military exercise between the U.S. and South Korea against North Korea at an undisclosed location in South Korea
A.P4 July 2017
North Korean Leader Kim Jong Un looks on during the test-fire of inter-continental ballistic missile Hwasong-14
Reuters4 July 2017
Russian President Vladimir Putin (R) shakes hands with his Chinese counterpart Xi Jinping during a signing ceremony following the talks at the Kremlin
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3 July 2017
Belarussian servicemen march during a military parade as part of celebrations marking the Independence Day in Minsk, Belarus
Reuters3 July 2017
Ambulance cars and fire engines are seen near the site where a coach burst into flames after colliding with a lorry on a motorway near Muenchberg, Germany
Reuters2 July 2017
Protesters demonstrating against the upcoming G20 economic summit ride boats on Inner Alster lake during a protest march in Hamburg, Germany. Hamburg will host the upcoming G20 summit and is expecting heavy protests throughout.
Getty Images1 July 2017
Protesters carry a large image of jailed Chinese Nobel Peace laureate Liu Xiaobo as they march during the annual pro-democracy protest in Hong Kong. Thousands joined an annual protest march in Hong Kong, hours after Chinese President Xi Jinping wrapped up his visit to the city by warning against challenges to Beijing's sovereignty.
AP30 June 2017
Jockey Andrea Coghe of "Selva" (Forest) parish rides his horse during the first practice for the Palio Horse Race in Siena, Italy June 30, 2017
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30 June 2017
A man takes pictures with a phone with a Union Flag casing after Chinese President Xi Jinping (not pictured) inspected troops at the People's Liberation Army (PLA) Hong Kong Garrison as part of events marking the 20th anniversary of the city's handover from British to Chinese rule, in Hong Kong, China June 30, 2017
Reuters29 June 2017
A protester against U.S. President Donald Trump's limited travel ban, approved by the U.S. Supreme Court, holds a sign next to protesters supporting the ban, in New York City, U.S., June 29, 2017
Reuters29 June 2017
Israeli Air Force Efroni T-6 Texan II planes perform at an air show during the graduation of new cadet pilots at Hatzerim base in the Negev desert, near the southern Israeli city of Beer Sheva
AFP/Getty Images28 June 2017
A woman gestures next to people spraying insecticide on a vehicle during a mosquito-control operation led by Ivory Coast's National Public and Health Institute in Bingerville, near Abidjan where several cases of dengue fever were reported
AFP/Getty Images28 June 2017
An aerial view shows women swimming in the Yenisei River on a hot summer day, with the air temperature at about 32 degrees Celsius (89.6 degrees Fahrenheit), outside Krasnoyarsk, Siberia, Russia, June 28, 2017
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27 June 2017
A Libyan coast guardsman watches over as illegal immigrants arrive to land in a dinghy during the rescue of 147 people who attempted to reach Europe off the coastal town of Zawiyah, 45 kilometres west of the capital Tripoli, on June 27, 2017. More than 8,000 migrants have been rescued in waters off Libya during the past 48 hours in difficult weather conditions, Italy's coastguard said on June 27, 2017
AFP/Getty Images27 June 2017
Investigators work at the scene of a car bomb explosion which killed Maxim Shapoval, a high-ranking official involved in military intelligence, in Kiev, Ukraine, June 27, 2017
Reuters26 June 2017
A man leaves after voting in the Mongolian presidential election at the Erdene Sum Ger (Yurt) polling station in Tuul Valley. Mongolians cast ballots on June 26 to choose between a horse breeder, a judoka and a feng shui master in a presidential election rife with corruption scandals and nationalist rhetoric
AFP/Getty Images26 June 2017
People attend Eid al-Fitr prayers to mark the end of the holy fasting month of Ramadan at a play ground in the suburb of Sale, Morocco
REUTERS25 June 2017
A plain-clothes police officer kicks a member of a group of LGBT rights activist as Turkish police prevent them from going ahead with a Gay Pride annual parade on 25 June 2017 in Istanbul, a day after it was banned by the city governor's office.
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25 June 2017
Pakistan army soldiers stands guard while rescue workers examine the site of an oil tanker explosion at a highway near Bahawalpur, Pakistan. An overturned oil tanker burst into flames in Pakistan on Sunday, killing more than one hundred people who had rushed to the scene of the highway accident to gather leaking fuel, an official said.
AP24 June 2017
Rescue workers search for survivors at the site of a landslide that occurred in Xinmo Village, Mao County, Sichuan province, China
REUTERS23 June 2017
Student activists shout anti martial law slogans during a protest in Manila on June 23, 2017
AFP/Getty Images23 June 2017
A diver performs from the Pont Alexandre III bridge into the River Seine in Paris, France, June 23, 2017 as Paris transforms into a giant Olympic park to celebrate International Olympic Days with a variety of sporting events for the public across the city during two days as the city bids to host the 2024 Olympic and Paralympic Games
Reuters23 June 2017
Debris and smoke are seen after an OV-10 Bronco aircraft released a bomb, during an airstrike, as government troops continue their assault against insurgents from the Maute group, who have taken over parts of Marawi city, Philippines June 23, 2017
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22 June 2017
Russian President Vladimir Putin (C) stands under pouring rain during a wreath-laying ceremony marking the 76th anniversary of the Nazi German invasion, by the Kremlin walls in Moscow, on June 22, 2017
AFP/Getty Images22 June 2017
Smoke rises following a reported air strike on a rebel-held area in the southern Syrian city of Daraa, on June 22, 2017
AFP/Getty Images22 June 2017
Iraqis flee from the Old City of Mosul on June 22, 2017, during the ongoing offensive by Iraqi forces to retake the last district still held by the Islamic State (IS) group
AFP/Getty Images21 June 2017
Girls stand in monsoon rains beside an open laundry in New Delhi, India
Reuters21 June 2017
People take part in the 15th annual Times Square yoga event celebrating the Summer Solstice, the longest day of the year, during classes in the middle of Times Square in New York. The event marked the international day of yoga.
ReutersSwipe to continue
20 June 2017
Faroe Islanders turn the sea red after slaughtering hundreds of whales as part of annual tradition
Rex20 June 2017
A firefighting plane tackles a blaze in Cadafaz, near Goes, Portugal
Reuters15 June 2017
A person participates in a journalists' protest asking for justice in recent attacks on journalists in Mexico City, Mexico, 15 June 2017
EPA11 June 2017
Poland's Piotr Lobodzinski starts in front of the Messeturm, Fairground Tower, in Frankfurt Germany. More than 1,000 runners climbed the 1202 stairs, and 222 meters of height in the Frankfurt Messeturm skyscraper run
AP11 June 2017
A runner lies on the ground after arriving at the finish line in Frankfurt Germany. More than 1,000 runners climbed the 1202 stairs, and 222 meters of height in the Frankfurt Messeturm skyscraper run
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11 June 2017
A troupe of Ukrainian dancers perform at Boryspil airport in Kiev, on the first day of visa-free travel for Ukrainian nationals to the European Union
Getty Images11 June 2017
A troupe of Ukrainian dancers perform on the tarmac at Boryspil airport in Kiev, on the first day of visa-free travel for Ukrainian nationals to the European Union
Getty Images11 June 2017
French President Emmanuel Macron with his wife Brigitte Trogneux cast their ballot at their polling station in the first round of the French legislatives elections in Le Touquet, northern France
EPA11 June 2017
A Thai worker paints on a large statue of the Goddess of Mercy, known as Guan Yin at a Chinese temple in Ratchaburi province, Thailand. Guan Yin is one of the most popular and well known Chinese Goddess in Asia and in the world. Guan Yin is the Bodhisattva of Great Compassion in Mahayana Buddhism and also worshiped by Taoist
EPA11 June 2017
A Thai worker paints on a large statue of the Goddess of Mercy, known as Guan Yin at a Chinese temple in Ratchaburi province, Thailand. Guan Yin is one of the most popular and well known Chinese Goddess in Asia and in the world. Guan Yin is the Bodhisattva of Great Compassion in Mahayana Buddhism and also worshiped by Taoists
EPASwipe to continue
10 June 2017
Volunteers spread mozzarella cheese toppings on the Guinness World Record attempt for the Longest Pizza in Fontana, California, USA. The pizza was planned to be 7000 feet (2.13 km) to break the previous record of 6082 feet (1.8 km) set in Naples, Italy in 2016
EPA10 June 2017
Jamaica's Olympic champion Usain Bolt gestures after winning his final 100 metres sprint at the 2nd Racers Grand Prix at the National Stadium in Kingston, Jamaica
REUTERS/Gilbert Bellamy10 June 2017
Usain Bolt of Jamaica salutes the crowd after winning 100m 'Salute to a Legend' race during the Racers Grand Prix at the national stadium in Kingston, Jamaica. Bolt partied with his devoted fans in an emotional farewell at the National Stadium on June 10 as he ran his final race on Jamaican soil. Bolt is retiring in August following the London World Championships
Getty Images10 June 2017
Usain Bolt of Jamaica salutes the crowd after winning 100m 'Salute to a Legend' race during the Racers Grand Prix at the national stadium in Kingston, Jamaica. Bolt partied with his devoted fans in an emotional farewell at the National Stadium on June 10 as he ran his final race on Jamaican soil. Bolt is retiring in August following the London World Championships
Getty Images10 June 2017
Police officers investigate at the Amsterdam Centraal station in Amsterdam, Netherlands. A car ploughed into pedestrians and injured at least five people outside the station. The background of the incident was not immediately known, though police state they have 'no indication whatsoever' the incident was an attack
EPASwipe to continue
10 June 2017
Police officers investigate at the Amsterdam Centraal station in Amsterdam, Netherlands. A car ploughed into pedestrians and injured at least five people outside the station. The background of the incident was not immediately known, though police state they have 'no indication whatsoever' the incident was an attack
EPA10 June 2017
Protesters stand off before police during a demonstration against corruption, repression and unemployment in Al Hoseima, Morocco. The neglected Rif region has been rocked by social unrest since the death in October of a fishmonger. Mouhcine Fikri, 31, was crushed in a rubbish truck as he protested against the seizure of swordfish caught out of season and his death has sparked fury and triggered nationwide protests
Getty Images9 June 2017
A man looks on at a migrant and refugee makeshift camp set up under the highway near Porte de la Chapelle, northern Paris
Getty Images9 June 2017
Damaged cars are seen stacked in the middle of a road in western Mosul's Zanjili neighbourhood during ongoing battles to try to take the city from Islamic State (IS) group fighters
Getty9 June 2017
Smoke billows following a reported air strike on a rebel-held area in the southern Syrian city of Daraa
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9 June 2017
Germany's Chancellor Angela Merkel gestures next to Mexico's President Enrique Pena Nieto during a welcome ceremony at the National Palace in Mexico City, Mexico
REUTERS/Carlos Jasso9 June 2017
Soldiers and residents carry the body of a Muslim boy who was hit by a stray bullet while praying inside a mosque, as government troops continue their assault against insurgents from the Maute group, who has taken over large parts of the Marawi City, Philippines
REUTERS/Romeo Ranoco8 June 2017
Opposition demonstrators protest for the death on the eve of young activist Neomar Lander during clashes with riot police, in Caracas
Getty Images8 June 2017
Neomar Lander, a 17-year-old boy was killed during a march in the Chacao district in eastern Caracas on Wednesday, taking the overall death toll since the beginning of April to 66, according to prosecutors
Getty Images8 June 2017
Former FBI director James Comey is sworn in during a hearing before the Senate Select Committee on Intelligence on Capitol Hill in Washington, DC
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8 June 2017
Former FBI Director James Comey testifies during a US Senate Select Committee on Intelligence hearing on Capitol Hill in Washington, DC
Getty Images8 June 2017
Usain Bolt of Jamaica trains at the University of West Indies in Kingston. Bolt says he is looking forward to having a party as he launches his final season on June 10 with what will be his last race on Jamaican soil. The 30-year-old world's fasted man plans to retire from track and field after the 2017 London World Championships in August
Getty Images8 June 2017
Acquanetta Warren, Mayor of Fontana, California, reacts after US President Donald Trump introduced himself before the Infrastructure Summit with Governors and Mayors at the White House in Washington, US
REUTERS/Yuri Gripas8 June 2017
Frenchman Alain Castany, sentenced to 20 years on charges of drug trafficking in the 'Air Cocaine' affair, leaves the prison in Santo Domingo, on his way to France, where he is being transferred for medical reason
Getty Images8 June 2017
A woman reacts at the place where 17-year-old demonstrator Neomar Lander died during riots at a rally against Venezuelan President Nicolas Maduro's government in Caracas, Venezuela, June 8, 2017. The sign reads: 'Neomar, entertainer for ever'
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30 July 2017
Soldiers of China's People's Liberation Army (PLA) get ready for the military parade to commemorate the 90th anniversary of the foundation of the army at Zhurihe military training base in Inner Mongolia Autonomous Region, China.
REUTERSAt least 70 people have been charged with terrorism since 2014, said Justice Minister Michael Keenan.
He added: "The primary threat to Australia still remains lone actors, but the events overnight remind us that there is still the ability for people to have sophisticated plots and sophisticated attacks still remain a real threat.
"In light of this information, it's very important that everyone in Australia remains vigilant."
Australian Federal Police commissioner Andrew Colvin said the investigation was likely to be “very long and protracted”.