Bahrain's influential Shiite opposition bloc Al-Wefaq and a more radical group have called separate rallies for Friday to protest the weekend staging of the Formula One Grand Prix in Manama.
Demonstrations have been held during the three-day Grand Prix event every year since 2011 by opponents of the ruling Sunni Al-Khalifa dynasty in an attempt to highlight pro-reform demands.
The protests, which first erupted in the wake of a Shiite-led uprising in February 2011, have at times been marred by violence but the race has never been affected.
They are mainly staged in Shiite villages surrounding Manama and away from the Sakhir F1 circuit in the capital's south.
The Bahrain Grand Prix practice sessions begin on Friday ahead of Sunday's race.
Al-Wefaq in a Tuesday statement urged its supporters to hold a rally on the main Budaya highway, four kilometres (2.5 miles) west of Manama, which links several Shiite villages.
Al-Wefaq's peaceful rallies are usually tolerated by the authorities and rarely end with clashes.
But protests by supporters of radical cyber-group the February 14 Revolution Youth Coalition are more violent and often end with clashes between police and demonstrators armed with petrol bombs.
The February 14 group, accused by authorities of links to Shiite-majority Iran, called on its Facebook page for demonstrations Friday in the Al-Seef Junction area, west of Manama, under the slogan: "Stop the blood formula."
Protests in Shiite villages surrounding Manama began this week, with witnesses reporting masked demonstrators staging rallies chanting: "No, no to Formula 1" and "Down Hamad," in reference to the king.
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The rallies have been broken up by police firing tear gas and stun grenades, with protesters hurling petrol bombs and throwing stones, according to witnesses.
Public security chief General Tariq Hasan said Tuesday the authorities have taken "all measures and plans" to secure the April 4-6 Formula One event.
Police will deploy around the Sakhir circuit and along main roads leading to it, the official BNA news agency quoted Hasan as saying.
Amnesty International raised concerns on Tuesday of a crackdown ahead of the Grand Prix.
"There are fears that the authorities may use recent unrest, including terror attacks on police, to justify imposing further restrictions during the Grand Prix," said the London-based human rights watchdog.
"Using the Grand Prix to boost Bahrain's public image is little more than a blatant attempt to gloss over mounting abuses with the hype of an international sporting event," said Amnesty's Said Boumedouha.
Celebrating the 10th anniversary of Bahrain's hosting of the event, the race will this year take place at night.
Bahrain, home to the US Fifth Fleet, remains deeply divided three years after the Shiite-led uprising was quashed, with persistent protests sparking clashes with police, scores of Shiites jailed on "terror" charges and reconciliation talks deadlocked.
The International Federation for Human Rights says at least 89 people have been killed in Bahrain since the uprising began in February 2011.