Riot police in Bahrain fired tear gas and stun grenades as tens of thousands of protesters staged the biggest anti-government demonstrations in weeks in the divided Gulf nation.
Opposition groups called for major rallies after a prominent rights activist, Nabeel Rajab, was placed back in detention earlier this week on fresh charges linked to his social media posts.
Bahrain has experienced near daily protests for 16 months caused by an uprising by the kingdom's Shiite majority seeking greater political rights from the Western-backed Sunni monarchy.
At least 50 people have died in the unrest since February 2011.
There were no immediate reports of injuries from the street battles, which left piles of burning rubbish and clouds of stinging tear gas in the western outskirts of the capital, Manama.
Bahrain's rulers have crucial support from neighbouring Saudi Arabia, but are under pressure from their US allies to reopen dialogue with Shiite opposition factions.
A new government initiative for talks is expected to be announced next week.
But main Shiite groups have already signalled that negotiations are futile unless the ruling dynasty agrees to give up its near total control of government affairs in the strategic island, which is home to the US navy's 5th Fleet.
Earlier, a defence lawyer said a court hearing is planned next week for an 11-year-old boy detained for allegedly taking part in the anti-government protests. The lawyer, Mohsen al-Alawi, said the student is scheduled to appear in court on Monday on charges of joining an illegal gathering and other claims related to the ongoing unrest.
Mr Al-Alawi said the boy, Ali Hasan, was arrested last month and took his school exams behind bars. He is among the youngest suspects detained in Bahrain's crackdowns.