Protesters have again clashed with police in Bahrain prior to the Formula One Grand Prix race there on Sunday.
Masked youths hurled petrol bombs at police, who stopped them marching to a traffic roundabout in the capital, Manama, that was a gathering point during an uprising last year. Police responded by firing tear gas and sound bombs.
The demonstrators are calling for democratic reforms in the Gulf kingdom.
The BBC reports the main demonstration on Friday had been sanctioned despite overnight clashes between security forces and protesters in several villages.
Crown Prince Salman bin Hamad Al Khalifa earlier guaranteed the safety of the racing drivers and teams, after a car carrying members of the Force India team was caught in clashes between police and protesters on Thursday and a petrol bomb exploded nearby.
The race circuit was built in 2003 at a cost of $US150 million and the first Grand Prix was held in 2004.
However, unrest in the kingdom forced a postponement and then the cancellation of the race last year after 35 people, including five police, were killed in demonstrations.
The Crown Prince says that cancelling the race this year would empower extremists.