Thousands of anti-government protesters have been dispersed after flooding a major highway in Bahrain demanding a halt to the Formula One race on the first day of its practice ahead of Sunday's race.
The move came as the Gulf kingdom's crown prince vowed that the country's premier sporting event would go ahead.
Bahraini authorities stepped up security around the Formula One circuit on Friday after clashes between protesters and security forces intensified ahead of the Grand Prix.
Friday's massive rally was organised by Shia political blocs, including the main groups al-Wefaq and al-Waad.
The rally is part of actions by the country's majority Shia population as they continue their longstanding demands for greater equality in the Sunni-ruled kingdom.
Al Jazeera's special correspondent in Manama, the capital, who cannot be named for security reasons, described the part of the protest that he followed:
"I would say about 3,000 people gathered with banners and chanting for freedom and democracy and dignity," he said.
"That demonstration has now been effectively disrupted by the police.
He said a "good deal" of the protesters were taking cover from the tear gas and riot police in a shopping mall.
'Entering a war'
The rally was given a permit by the government, but riot police fired stun grenades and tear gas at a group of about hundred protesters who broke away from the rally and headed to Pearl Square, the now heavily guarded roundabout in the capital that had served as the opposition's hub during the first weeks of last year's uprising.
Sheik Isa Qassim, Bahrain's most senior Shia cleric, condemned the Sunni rulers for staging the race despite opposition protests.
In a strongly worded sermon during Friday prayers, the cleric said the rulers have cracked down on dissent aggressively ahead of the event "as if we are entering a war".
The race is Bahrain's premier international event, part of the tiny island kingdom's attempts to boost its prestige in recent years.
Last year's race was cancelled because of unrest in the country. Protests began in February, 2010, and were met with a crackdown in which 35 people, including security personnel, died.
The 2012 race is going ahead despite appeals by rights groups for another cancellation and pressure from protesters, including a jailed activist who is on a more than two-month-long hunger strike.
Clashes between protesters and security forces have taken place almost every day for months.
The unrest has intensified in the lead-up to the race, including riot police clashing with opposition supporters in the predominantly Shia villages that ring Manama.
Al-Wefaq leaders said at least 50 people have been injured in the past two days when security forces fired pellets to disperse protesters on several occasions.
Additional security forces were deployed this week, setting up checkpoints on Friday on roads leading to the Bahrain International Circuit, the location of the race, and increasing their presence across the capital.
'Force for good'
The rulers have depicted the race - expected to draw a worldwide TV audience of about 100 million in 187 countries - as an event that will put the divided society on the path of reconciliation.
During a visit to the circuit on Friday, Crown Prince Salman bin Hamad Al Khalifa, who owns the rights to the event, told reporters that the race should go ahead.
"I genuinely believe this race is a force for good, it unites many people from many different religious backgrounds, sects and ethnicities," Salman said.
On the track, teams were practicing on Friday ahead of Saturday's qualification race.
"I think there's too much money involved in this and I think we're too far down the road for them to cancel [the race]," said our special correspondent.
Last year, Salman was tasked to lead a national dialogue aimed at reconciliation between Shia and Sunnis. The talks broke down without any compromise and have not yet resumed.
Meanwhile, Iraqi hardline Shia cleric Muqtada al-Sadr denounced Bahrain for staging the Grand Prix while "blood is being shed" on the island.
Sadr also condemned the teams for racing, saying their presence in Bahrain gives "support for injustices and the killings".