Bahraini security forces clashed with protesters against Bahrain's controversial Grand Prix in Shiite villages on Friday despite beefed up security for the start of practice sessions.
The overnight clashes between protesters and security forces across Shiite villages continued into the early morning, witnesses said.
"The people want to topple the regime," chanted dozens of protesters carrying pictures of jailed hunger striker Abdulhadi al-Khawaja. "Down Hamad," they called, referring to Bahrain's king.
Met by tear gas and sound bombs, the protesters responded by hurling petrol bombs at security forces, witnesses said. Security forces also fired buckshot to disperse the crowds, wounding dozens of people.
Protesters burned tyres, briefly blocking several main roads leading to the Sakhir circuit where Friday's Formula One practices were taking place, witnesses said.
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The February 14 Youth Movement had called on social networking sites for "three days of rage" to coincide with the event.
And Bahrain's main opposition group, Al-Wefaq, called for a week of daily protests to coincide with the Grand Prix, to focus media attention on their longstanding demands for greater equality in the Sunni-ruled kingdom.
The government has barred the opposition from holding protests in Manama itself.
Earlier this week, hundreds of protesters marched carrying banners held a demonstration near Bahrain's international airport as the race teams flew in, despite the arrest of about 80 leading pro-democracy activists.
The Bahrain Grand Prix was cancelled last year in the wake of a Shiite-led uprising against the Sunni monarchy and the brutal government crackdown that followed in which a government commission said 35 people were killed.