Activists called for a new attempt to march on the Bahraini capital's former Pearl Square protest hub on Saturday amid tight security for the F1 Grand Prix and after an overnight attack on police injured two people.
Hundreds took to the streets in several Shiite villages, prompting late-night clashes with police, but away from the Sakhir racing circuit south of Manama where Sunday's Grand Prix race will be staged, witnesses said.
"Your race is a crime," chanted protesters armed with petrol bombs and stones. "No, no to blood Formula."
Police responded with tear gas and stun grenades.
In a statement on Twitter, the interior ministry announced late on Friday that "targeting police patrols with Molotov cocktails on Isa Al-Kabeer road led to injuring two Asians."
It said the pair were taken to hospital, but the extent of their injuries was not known.
The radical February 14 Revolution Youth Coalition, a clandestine cyber-group that had called a week-long campaign dubbed "Volcanic Flames", urged supporters on Twitter to march on the focal point of Shiite-led protests in early 2011.
"We will march today Saturday towards the epicentre of the revolution," the group announced.
Police on Friday fired tear gas and birdshot to disperse protesters trying to stage a similar march to the roundabout formerly known as Pearl Square before authorities razed it after a crackdown on the Shiite-led February-March 2011 protests.
Journalists heading to the Sakhir circuit for Saturday's practice said the Pearl Square area had completely cordoned off by cement blocks.
Police were out in force early on Saturday, with several armoured vehicles deployed around Pearl Square, and along the highway leading to the circuit.
Opposition demonstrators have been protesting to highlight pro-reform demands and have urged solidarity from teams taking part in Sunday's race.
Supporters of the February 14 movement have campaigned for the race to be cancelled, calling it a "crime".
Sunday's race is seen as a boost to the image and economy of the tiny Gulf monarchy that has a Shiite Muslim majority but is ruled by a Sunni dynasty and which has been rocked by continuing Arab Spring-inspired unrest.
Security forces have been on high alert during days of protests to prevent clashes from marring the race, with checkpoints at major intersections, especially on roads leading to the racing circuit.
World motorsport's governing body the FIA and promoters Formula One Management said Sunday's race would take place despite the demonstrations.
"The Federation Internationale de l'Automobile and Formula One Management wish to jointly confirm their belief that the Bahrain GP should go ahead this weekend, following assurances from the local promoter and the authorities that security, their responsibility, will be guaranteed for all participants," a statement read.
The event was cancelled in 2011 but took place as scheduled last year.
The month-long 2011 protests in Bahrain, home to the US Navy's Fifth Fleet, were crushed with the help of Gulf troops led by neighbouring Saudi Arabia.
Strategically located across the Gulf from Shiite-ruled Iran, Bahrain has continued to see sporadic protests, mostly outside Manama, and rights groups say a total of 80 people have been killed in the unrest since February 2011.