Bahrain anti-government activists have clashed with police and blocked roads into the capital, in a bid to disrupt the Formula 1 Grand Prix.
The protesters accuse the government of using the race to gain international recognition and cover up rights abuses.
Bahrain's Crown Prince Salman says a reform process is under way, and denies using Formula 1 for political gain.
Witnesses said access to the Formula 1 event had been largely unaffected by the demonstrations.
The island nation has been convulsed by protests since early 2011, in which dozens of people have died.
The protesters are drawn from the majority Shia population, and they are demanding greater rights from the ruling Sunni royal family.'Race of blood'
Early on Sunday groups of young men gathered and blocked roads into the capital with barricades of burning tyres.Continue reading the main story
The police clashed with the demonstrators and fired tear gas to disperse the crowds.
Youths threw stones and petrol bombs in response, according to witnesses.
Sporadic clashes have taken place over the past few days in villages around the capital.
Protesters have chanted slogans including "your race is a crime" and "no, no to the race of blood".
Formula 1 boss Bernie Ecclestone said on Saturday that the race had given the protesters a platform.
"The government here were stupid, in a lot of ways, to put this race on," he said.
But he added: "I don't think it's for us to decide the politics, good or bad. It's a good circuit, a good race, and we think everybody's happy so we're here."
Crown Prince Salman has insisted that the race reflects passion for sport and has nothing to do with politics.
Analysts say the crown prince is a reformist in a government divided on how to respond to opposition demands.
The two sides have held talks, but the opposition has stated repeatedly that the talks cannot succeed without a senior member of the ruling family.
Hardliners loyal to unelected Prime Minister Sheikh Khalifa bin Salman al-Khalifa, who has been in his post since 1971, are said to be hindering the dialogue process.
They fear that offering any concessions will erode their power and encourage more demands.
The race, which was first run in Bahrain in 2004, was cancelled two years ago following the forced clearance of a Manama landmark, Pearl Roundabout.
In the unrest that followed more than 50 people died, hundreds were arrested and thousands dismissed from their jobs.
The government has since launched an inquiry and says that nearly all those dismissed have been reinstated.