Bahraini protesters blocked roads and clashed with police at dawn on Sunday, only hours ahead of the Gulf state's Formula One Grand Prix, but the authorities said the race would go ahead without incident.
Masked youths demonstrating against the staging of the race set alight tyres on roads in villages populated by Shiite Muslims just outside Manama, according to witnesses.
But access was still open to the Sakhir circuit, south of the Bahraini capital.
Overnight, police fired tear gas in order to disperse demonstrators protesting in several Shiite-populated villages, chanting against the "race of blood," witnesses reported.
Shiite-led protests have intensified against Bahrain's Sunni rulers in the lead-up to this weekend's Grand Prix, a flagship event that has been dogged by controversy.
Bahrain's public security chief, Major General Tariq Hassan, spoke of stepped up measures to ensure a smooth race.
"Police are out in force to beef up security measures at the Bahrain International Circuit", he said in a statement.
"Security forces are deployed in all regions countrywide, undertaking pre-emptive and precautionary measures to ensure citizens and residents’ safety and security and protect public and private properties", he added.
Moderate opposition activists in Bahrain have been calling for more democracy, while youths of the radical February 14 Movement are demanding the fall of the regime.
The youth movement has called on its supporters to demonstrate in Shiite villages on Sunday afternoon, when the race is set to begin at 3:00 pm (1200 GMT).
Human rights groups say violence has killed at least 80 people in Bahrain since 2011, when month-long protests dominated by Shiites were brutally quelled by authorities of the kingdom ruled by the Sunni Al-Khalifa dynasty.
The latest clashes have renewed controversy over motor motor racing bosses' decision to keep Bahrain on the Formula One calendar despite similar disturbances that clouded the event last year.