Police in Bahrain have used tear gas and sound bombs to break up one of the island kingdom's largest anti-government rallies in weeks.

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.

Mazen Mahdi, a Bahraini photojournalist, said that media were stopped by police while covering the march.

There were also clashes in Jidhafs, a village near the capital Manama, and in Abu Saiba, a village west of Manama. At least one person in Jidhafs was injured by birdshot fired by riot police, according to Yousif al-Muhafdah, a Bahraini human rights activist.

Earlier on Friday, a defence 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 an illegal protest.

The boy, Ali Hasan, 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; unauthorised marches are quickly dispersed by police.

Opposition activists, most of them from Bahrain's Shia 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 criticise Bahrain's security forces over their increasing use of tear gas, arbitrary detentions, and ongoing claims of torture.