At least three people are dead after riot police stormed through a pro-democracy camp the capital of Bahrain.
Hundreds of riot police using tear gas and batons moved into Pearl Square in Manama before dawn on Thursday where thousands of people had earlier taken part in a third day of rallies.
The protesters in the small island kingdom are calling for democratic reform, the release of political prisoners and an end to what they call civil rights abuses.
Witnesses say up to 95 protesters have been wounded. Demonstrators fled pursued by security forces, as a helicopter flew overhead.
At the city's main Salmaniya hospital, medical staff were overwhelmed as ambulances and private cars still ferried in the injured more than three hours after the assault began, the ABC reports.
During the operation, explosions and ambulance sirens could be heard a few hundred metres from the central square, which has been sealed off.
About 2000 people had stayed overnight in Pearl Square. A member of the secular Waad party says police acted without any warning and there was a dense fog of tear gas where hundreds of women and children are camping.
A journalist with the American Broadcasting Corporation, Miguel Marquez was in Pearl Square when police arrived and was beaten after reporting on events, ABC says.
Since independence from the United Kingdom in 1971, tensions between the ruling Sunni elite and the Shia majority have frequently caused civil unrest. Shia groups say they are marginalised, subject to unfair laws, and repressed.
The protesters are adamant they will achieve the same success as demonstrators in Egypt, where president Hosni Murbarak was forced from power.
Protests linked to recent events in Egypt and Tunisia are gaining momentum across the Middle East and North Africa.
There have been violent clashes in Libya and other significant protests are continuing in Iran and Yemen.