The White House has reacted to the shooting down of Malaysian Airlines flight MH17 over Ukraine by criticising Russia's support for separatist rebels and urging the Kremlin to take "concrete steps" to ease tensions in the country.
A series of remarks by Barack Obama, Joe Biden and John Kerry stopped short of directly blaming pro-Russia rebels for the missile attack on a civilian airliner that killed 298 people.
But Hillary Clinton, the former US secretary of state, was more potent in her statements, saying in a television interview that indications pointed at the Russian-backed side and action was needed to "put [Vladimir] Putin on notice that he has gone too far and we are not going to stand idly by".
Clinton said in an interview with Charlie Rose on the American PBS network: "The questions I'd be asking is, number one, who could have shot it down? Who had the equipment? It's obviously an anti-aircraft missile. Who could have had the expertise to do that? Because commercial airlines are big targets, but by the time they got over that part of Ukraine they should have been high, so it takes some planning [to target such a plane].
"And the Ukrainian government has been quick to blame it on terrorists, which is their name for the Russian insurgents. And there does seem to be some growing awareness that it probably had to be Russian insurgents.
Hillary Clinton said Russian-backed rebels were most likely responsible for shooting down Malaysia Airlines flight MH17 over Ukraine. Video: Courtesy of Charlie Rose/Reuters"Now, how we determine that will require some forensics, but then if there is evidence pointing in that direction, the equipment had to have come from Russia. What more the Russians may or may not have done, we don't know.
"Europeans have to be the ones to take the lead on this. It was a flight from Amsterdam to Kuala Lumpur over European territory. There should be outrage in European capitals."
Joe Biden, the vice-president, said the plane had "apparently had been shot down. Shot down, not an accident. Blown out of the sky."
"We see reports that there may have been American citizens on board and obviously that's our first concern. And we are now working every minute to confirm those reports as I speak," Biden said at the start of a conference address in Detroit.
"This is truly a grave situation. Nearly 300 souls have been lost. The families have our consolation and our prayers. And there are many of them who need answers, and we will get those answers and we will take the next steps accordingly. We are in touch with the Ukrainian government, I was on the phone as I said for the better part of half an hour with President Poroshenko, I'm in contact with our president, as well as our national security team."
The White House press office issued a statement that did not directly blame the Russian side in the conflict but said: "While we do not yet have all the facts, we do know that this incident occurred in the context of a crisis in Ukraine that is fuelled by Russian support for the separatists, including through arms, materiel and training."
"This incident only highlights the urgency with which we continue to urge Russia to immediately take concrete steps to de-escalate the situation in Ukraine and to support a sustainable ceasefire and path toward peace that the Ukrainian government has consistently put forward."
The president, Barack Obama, who spoke to the Russian president, Vladimir Putin, by telephone, referred to the "terrible tragedy" and said efforts were under way to determine whether Americans had been killed. "The world is watching," he said during a speech in Delaware. "The United States will offer whatever assistance we can to determine what happened and why, and as a country our thoughts are with all the families of the passengers wherever they call home."
In its press statement the White House said: "We continue to seek information to determine whether there were any American citizens on board.
"It is critical that there be a full, credible and unimpeded international investigation as quickly as possible. We urge all concerned – Russia, the pro-Russian separatists, and Ukraine – to support an immediate ceasefire in order to ensure safe and unfettered access to the crash site for international investigators and in order to facilitate the recovery of remains.
"It is vital that no evidence be tampered with in any way and that all potential evidence and remains at the crash site are undisturbed. The United States remains prepared to contribute immediate assistance to any international investigation, including through resources provided by the NTSB and the FBI."
John Kerry, the secretary of state, said the US sent its condolences to the victims' families and the countries involved, and would help with the international investigation.