Bahrain, home to an often disgruntled Shi'ite majority, quelled protests in March that had demanded greater political freedoms, a constitutional monarchy and an end to sectarian discrimination.

Neighbouring Sunni-led Gulf states sent troops to back Bahrain's forces, in turn boosting regional tension with nearby Shi'ite power Iran, which Bahrain accuses of manipulating its Shi'ite co-religionists to expand its influence.

Since then, Bahrain has launched a rolling crackdown targeting those who took part in the protests. Hundreds have been arrested and dozens put on trial in special courts, while others have been fired from government jobs.

The government says it only targets those who committed crimes during the unrest. It has said about 400 people detained in the aftermath of the protests will face prosecution.

At least 29 people, all but six of them Shi'ites, have been killed since the protests started in February, inspired by Arab revolts against autocratic rule that toppled the rulers of Egypt and Tunisia.

The six non-Shi'ites killed included two foreigners - an Indian and a Bangladeshi - and four policemen.