Race day of the Bahrain Formula One Grand Prix was set to go ahead on Sunday despite pressure for the event to be cancelled over violence that has killed one person in the Gulf kingdom.
King Hamad announced, meanwhile, that he would be attending the highly controversial race, in an apparent effort to allay security concerns even as clashes broke out overnight in the kingdom's Shiite villages.
Bahrain insists the unrest is isolated, but tensions have mounted as majority Shiites protest against their Sunni rulers, taking advantage of the media spotlight on one of the Gulf state's showcase events.
In a statement issued early on Sunday, King Hamad said he would be attending "the climax of the three-day event," and pledged he was committed to reform efforts in the kingdom.
"I also want to make clear my personal commitment to reform and reconciliation in our great country. The door is always open for sincere dialogue amongst all our people," said the monarch.
His announcement came as police fired tear gas and stun grenades at Shiite protesters who responded by hurling rocks and fire bombs while chanting "Down with Hamad," witnesses told AFP.
Security was heavy around Shiite villages in anticipation of demonstrations called for by the February 14 Youth Movement, who have boycotted the race and pledged "three days of rage" to coincide with the Grand Prix.
In protests that lasted through the night and into the early hours Sunday, demonstrators also called for the release of prominent Shiite activist Abdulhadi al-Khawaja, on hunger strike since early February and whose deteriorating health has raised fears he may die in prison.
In a message posted on micro-blogging website Twitter, Bahrain's interior ministry said on Sunday that Khawaja was in "good health" and would meet Denmark's ambassador today." Khawaja is a dual citizen of Bahrain and Denmark.
Rights watchdogs have repeatedly called for Khawaja's release and denounced the government's reforms as mostly hollow, cautioning the continued political stalemate could set the country on a path to more violent confrontation.
Last week, the International Crisis Group think tank issued a conflict risk alert for Bahrain, arguing that the decision to stage the F1 race and Khawaja's imprisonment were both ticking "time bombs" in the kingdom's 14-month uprising.
The Sakhir circuit, where the race is set to start at 1200 GMT on Sunday, has been under a total lockdown since late Saturday.
But witnesses said protesters were briefly able to block some roads leading to the track on Saturday night, setting tyres and garbage on fire.
In some Shiite villages, including Malkiya, Karzakan, Sadad and Damistan, protesters carried banners that read "No to the formula of blood," a key campaign slogan of the February 14 movement.
In the capital Manama, meanwhile, police prevented planned protests at a central market, residents and witnesses said.
The latest clashes come a day after a protester was found dead in the Shiite village of Shakhura, where the opposition Al-Wefaq movement said security forces on Friday night "attacked peaceful protesters, brutally beating some of them with various tools and weapons."
The interior ministry said an investigation was under way into the death of 36-year-old Salah Abbas Habib, which was being treated as a murder.
The violence has been centred mostly in and around Manama's neighbouring Shiite villages but on Wednesday, four mechanics from the Force India team were caught in a traffic jam as a petrol bomb exploded nearby.
Since, two team members left the country and the Force India crew cancelled Friday afternoon's practice run.