Bahrain's Shiite opposition was to gather Friday after a night of clashes for mass rallies coinciding with the start of Formula One Grand Prix practice sessions, seeking to highlight their pro-reform demands.
The radical February 14 Revolution Youth Coalition, a clandestine cyber-group, called for Friday to be a "Day of Rage," urging demonstrators to take to the streets against the "blood Formula". Other opposition groups also called for protests but urged that they be peaceful.
The rallies come after clashes into the night Thursday in several areas across Bahrain, with witnesses reporting police firing stun grenades and tear gas at protesters who burnt tyres, blocked main roads and threw stones and petrol bombs at security forces.
"No Formula on Bahrain's occupied land," chanted the protesters. "No, no blood Formula."
The clashes however remained away from roads leading to the Sakhir circuit south of Manama, where Sunday's race is taking place.
Security forces are on high alert to prevent possible clashes from marring the race. The event is seen as a booster to the image and economy of the tiny Gulf monarchy torn by Arab Spring-inspired unrest.
Checkpoints were set up at major intersections, particularly on roads leading to the Sakhir circuit.
The February 14 group said on Twitter its supporters had burned tyres and blocked major roads during the night. Witnesses confirmed that protesters had blocked roads near Bahrain International Airport.
Supporters of the more moderate Shiite opposition group Al-Wefaq had gathered in a peaceful protest in the village of Karzakan, three kilometres (1.3 miles) from Sakhir.
Al-Wefaq called further protests on Friday, urging on its Twitter page that participants demonstrate in a "disciplined and civilised way that suits our people."
Sunni-ruled Bahrain, home to the US Navy's Fifth Fleet, was rocked by month-long protests led by the kingdom's Shiite majority in early 2011. They were crushed with the help of Gulf troops led by neighbouring Saudi Arabia.
Al-Wefaq members have repeatedly said they do not oppose the event but want their protests to be heard internationally and to press for solidarity from participating teams.
Government spokeswoman Samira Rajab said: "Bahrain is ready to host the F1 and there are no security issues," dismissing the protests as "childish movements implementing Iranian agendas... that will not affect the race."
Police have been rounding up pro-democracy activists in an attempt to head off protests.
On Thursday, Human Rights Watch accused Formula One of "ignoring rights abuses". Security forces in Bahrain had "increased their repressive actions in the lead up to the 2013 race," the group added.
Bahrain International Circuit chairman Zayed Alzayani said he hoped to fill the grandstands and to have a crowd of more than 25,000 at the race day on Sunday, insisting it was safe to go ahead with the race.
Alzayani said he and organisers were focused on ensuring that the race passed off without incident.
"Our job is to make sure the event passes smoothly," he added. "We do our part and whatever happens outside the track, somebody else is responsible for."
The event was cancelled in 2011 but went ahead last year.
Strategically situated across the Gulf from Shiite-ruled Iran, Bahrain has continued to witness sporadic demonstrations, now mostly outside the capital.
Human rights groups say a total of 80 people have been killed in the unrest in Bahrain since February 2011.