Mass protests were under way in Bahrain after activists and opposition members launched "three days of rage" in protest against the Bahraini Grand Prix.
Tens of thousands of Bahrainis took to the streets to march on the Formula One Grand Prix circuit.
The capital of Manama was the focal point for protests but smaller demonstrations took place in surrounding villages.
Authorities tightened security after violent clashes with angry protesters over the last few days. Roads into the capital were blocked by security forces.
Activists warned they would defy attempts to prevent them from reaching Manama.
They accused security forces of putting up barbed wire around Shia villages and of using teargas on demonstrators.
On Twitter, they reported teargas volleys and claimed children had suffocated. The claims could not be independently verified.
The Grand Prix was surrounded by even more controversy after it emerged that several foreign journalists had been prevented from entering the country to cover the event.
Cameramen already in Bahrain were required to put fluorescent orange stickers on their cameras to identify them. They have been banned from covering any off-track events, such as protests, AP reported.
Protesters have called for the cancellation of the race in protest at what they say is a systematic government-led crackdown on the opposition.
Bahrain's Crown Prince Sheikh Salam bin Hamad al Khalifa, who was a few days ago confronted by protesters, said that cancelling the race would only "empower terrorists".
"For those of us trying to navigate a way out of this political problem, having the race allows us to build bridges across communities, to get people working together. It allows us to celebrate our nation. It is an idea that is positive, not one that is divisive," he added.