Clashes have escalated in the run-up to this weekend's Grand Prix race
Heavy clashes between anti-government protesters and security forces continued into the night in Bahrain, ahead of Sunday's F1 Grand Prix.
Demonstrators blocked roads with burning tyres, and police fired tear gas and stun grenades, as violence over the past week intensified.
A Friday rally called by the main opposition party al-Wefaq has drawn thousands of protesters.
The peaceful march has blocked a major motorway in the capital Manama.
Some of the crowd carried banners with the slogan: "Don't race on our blood."
Activists have demanded that F1 bosses cancel the race due to Bahrain's poor human rights record.
But in a joint statement, motorsport's world governing body and Formula One management said the race should go ahead as planned.
The Federation Internationale de l'Automobile (FIA) and Formula One Management (FOM) said they "also strongly believe sport can often be a force for good and that the staging of the Grand Prix in Bahrain will come some way in helping soothe some of the issues which have been raised in the media".
The Bahrain Center for Human Rights says 13 people have been arrested and that clashes were continuing in villages close to the Sakhir track, the site of the race, south of the capital, Manama.
A centre spokesperson said police had fired tear gas and birdshot against protesters in the towns of Sitra and Diraz.
Protests were reported across the kingdom on Thursday night, with demonstrators chanting "No Formula on Bahrain's occupied land", according to AFP news agency.
The authorities are anxious for the race to pass off without incident, and checkpoints have been set up at junctions leading to the track, AFP reports.
F1 practice sessions are being held at the circuit on Friday, ahead of qualifying rounds on Saturday.
Al-Wefaq says more than 100 people have been arrested this month, many from the villages near the circuit.
The organisation says peaceful protesters should come out in force on Friday, but it has not called for the race to be cancelled.
For the past two years members of the Shia majority have been protesting against alleged human rights abuses by the ruling Sunni minority.
The latest clashes come after days of escalating tensions.
On Tuesday, police fired tear gas and clashed with students in a raid on a secondary school in the capital, Manama.
Officers stormed the Jabreya school for boys after students staged a protest demanding the release of a colleague arrested on Monday, activists say.
On Sunday a car bomb blew up in the heart of the financial district in Manama, though without causing injuries.
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