Bahrain's riot police fired teargas and stun grenades on Friday to disperse tens of thousands of protesters who staged the biggest anti-government demonstrations in weeks.

Bahrain Bahrain protests Al-Khalifa Al-Saud Manama people Bahrain the Bahrain Bahrain's Shiites

Witnesses on Friday said there were demonstrations in nearly a dozen locations. The largest was a group of thousands of protesters who marched down Budaiya highway, a major road outside the capital which has seen frequent unrest since the uprising in Bahrain began nearly 18 months ago. The rally was abruptly ended when riot police fired tear gas.

There were also clashes in Jidhafs, a village near the capital Manama, and in Abu Saiba, a village West of Manama.

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 posts on social media such as Twitter.

There were no immediate reports of injuries from Friday's street battles, which left piles of burning rubbish and clouds of stinging tear gas in the western outskirts of the capital, Manama.

The media were stopped by police while covering the march.

Earlier on Friday, a defense lawyer told reporters that a court hearing had been scheduled for next week in the case of an 11-year-old boy accused of participating in a protest.

The boy, Ali Hassan, was arrested last month. He took school exams while behind bars, according to his lawyer, Mohsen al-Alawi.

Protests in Bahrain erupted in February of 2011, and they have continued almost daily ever since. The government tries to keep protesters confined to their villages; marches are quickly dispersed by police.

Opposition activists, most of them from Bahrain's Shiite majority, complain of longstanding discrimination by the ruling Sunni monarchy. An official commission which studied the unrest released a scathing report in November which accused the government of widespread human rights abuses.

The government claims to have implemented reforms, but opposition activists argue that most have been merely cosmetic. Human rights groups continue to criticize Bahrain's security forces over their increasing use of tear gas, arbitrary detentions, and ongoing torture.