Protesters clashed with riot police in Bahrain overnight, witnesses said on Saturday, raising security fears ahead of this weekend's Formula One Grand Prix race in the Gulf kingdom.
Dozens of people took to the streets late on Friday and set alight tyres near the villages of Damistan, Karzakkan, Malkiya and Sadad, all less than four kilometres (2.5 miles) from the Sakhir Grand Prix circuit.
"Down with Hamad," they chanted, referring to Bahrain's king, along with other slogans in support of jailed Shiite activist Abdulhadi al-Khawaja, who has been on a hunger strike for two months.
Some of the protesters, who included women, wore face masks and several were dressed in white shrouds bearing the message: "I am the next martyr."
Security forces fired tear gas and sound bombs to disperse the demonstrators, some of whom responded by hurling petrol bombs and stones, witnesses said, adding that the clashes were "violent."
No casualties were reported, however.
The clashes followed a massive afternoon demonstration in the Shiite suburb of Budaya, west of Manama.
Shiite-led protests have intensified in Bahrain, site of a month-long uprising that was crushed last year, since its Sunni rulers insisted on going ahead with the Grand Prix despite pressure to call it off.
The February 14 Youth Movement has called on social networking sites for "three days of rage" to coincide with the race.
Bahrain's main opposition group, Al-Wefaq, had called for a week of daily protests during the event to focus media attention on their long-standing demands for reforms.
But on Friday, when F1 teams took to the track for the first free practice sessions, Crown Prince Salman bin Hamad Al-Khalifa ruled out cancelling the event.
"I think cancelling just empowers extremists," he told a media briefing at Sakhir.
"I think for those of us who are trying to navigate a way out of this political problem, having the race allows us to build bridges across communities, and get people working together."
His remarks came after Force India team said that, "for logistical reasons," it would not take part in Friday's second practice session "to ensure the most competitive performance in FP3, qualifying and the race."
Deputy team principal Bob Fernley had told Autosport magazine they were considering curtailing practice in order to return to their hotel before dark but that they would not miss qualification on Saturday or Sunday's race.
Four Force India team members were caught up in a confrontation between protesters and police on Wednesday when a petrol bomb exploded near their car.
Two team members chose to leave Bahrain on Thursday.
And the Sauber team confirmed on Friday that they drove through a similar incident the previous day, but that none of the 12 mechanics in an unmarked mini-bus was hurt.
As second practice continued, Formula One's chief executive and commercial ringmaster Bernie Ecclestone also appeared unmoved about escalating safety concerns.
He said he did not understand why Force India was so worried about safety, adding he had personally offered to drive with the team from the circuit if they wanted reassurance.
"They have asked and been told they can have security if they want it," he said. "None of the other teams seem to have a problem."
McLaren team principal Martin Whitmarsh said all 10,500 seats in the main stand had been sold "which shows that the race is welcomed by many people at all levels of society. But often in this type of situation the voice of the majority is not heard."
Amid unease among Grand Prix participants, with Force India's British driver Paul Di Resta acknowledging it was an "uncomfortable situation," Prince Salman accepted that some teams had safety and security concerns.
"I absolutely can guarantee that any problems that may or may not happen are not directed at F1," he said. "It goes to show that there are people who are out to cause chaos.
"The attack that happened around Force India was aimed at the police. It was unprovoked and it was quite dangerous. But at no time was anyone from F1 in danger."
The Bahrain event was cancelled last year in the wake of and uprising and the government crackdown that followed in which a government commission said 35 people were killed.
Following Friday's free practice sessions, competition gets underway on Saturday for grid positions in the actual race on Sunday.