MANAMA, Bahrain -- Tens of thousands of anti-government protesters on Friday flooded onto a major highway in Bahrain demanding a halt to the Formula One race on its first day of practice runs, as the Gulf kingdom's crown prince vowed the country's premier prestige sporting event would go ahead.
Bahraini authorities stepped up security around the Formula One circuit after clashes between protesters and security forces intensified ahead of Sunday's Grand Prix race.
Last year, a wave of anti-government protests by the island's Shiite majority and a violent crackdown by the Sunni rulers forced organizers to cancel the 2011 Bahrain GP. At least 50 people have been killed since the start of Bahrain's uprising, inspired by other Arab Spring revolts, and violence continues to roil the island.
Friday's massive rally was organized by Shiite political blocs, including the main groups Al Wefaq and Al Waad. Protesters shouted slogans against the ruling Sunni dynasty, the main backer of the F1 race. The crown prince owns the rights to the event.
"We demand democracy" and "Down, Down Hamad," opposition supporters chanted in reference to King Hamad bin Isa Al Khalifa, as they massed on the main highway leading out of the capital, Manama, about 12 miles north of the Formula One track.
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 opposition's hub during the first weeks of last year's uprising.
There were no immediate reports of injuries.
Bahrain's most senior Shiite cleric, Sheik Isa Qassim, condemned the Sunni rulers for staging the F1 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 Grand Prix is Bahrain's premier international event, part of the tiny island kingdom's attempts to boost its prestige in recent years. The 2012 race is going ahead despite appeals by rights groups for another cancellation and pressure from protesters, including a jailed activist on a hunger strike that has lasted more than two months.
There have also been allegations of widespread human rights abuses in the tiny, but strategic island that is the home of the U.S. Navy's 5th Fleet.
To protest the race going forward, the hacking collective Anonymous claimed responsibility for a denial-of-service attack Friday on the official Formula One website that made Formula1.com unavailable to many users. The group also attacked F1-racers.net, where it posted a message saying the "Formula 1 racing authority was well-aware of the Human Rights situation in Bahrain and still chose to contribute to the regime's oppression of civilians and will be punished."
Shiites account for about 70 percent of Bahrain's population of just over half a million people, but claim they face widespread discrimination and lack the same opportunities as the Sunni minority. The country's leaders have offered some reforms, but the opposition says they fall short of Shiite demands for a greater voice in the country's affairs and an elected government.
Clashes between protesters and security forces have taken place almost daily for months. The unrest has intensified in the lead-up to the F1 race, including riot police clashing with opposition supporters in the predominantly Shiite 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 deployed this week, setting up checkpoints Friday on roads leading to the Bahrain International Circuit and increasing their presence across Manama.
The nation's 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 told reporters the F1 race should go ahead Sunday.
"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 Friday ahead of Saturday's qualification race.
In the past weeks, much of the protesters' anger has been directed at the crown prince, who is also the commander of the kingdom's armed forces, which the opposition supporters say have been enforcing the crackdown.
Last year, Salman was tasked to lead a national dialogue aimed at reconciliation between Shiite and Sunnis. The talks broke down without any compromise and have not yet resumed.
In Iraq, hard-line Shiite cleric Muqtada al-Sadr denounced Bahrain for staging the Grand Prix while "blood is being shed" on the island. Al-Sadr also condemned the F1 teams for racing, saying their presence in Bahrain gives "support for injustices and the killings."
As a majority Shiite country, Iraq has backed Bahrain's Shiite-led protests.