Security forces in Bahrain have used tanks, water cannon and helicopters to disperse anti-government demonstrators in the capital Manama.
The forces cleared hundreds of people from a camp in the capital that had become the symbol of an uprising by the Shi'ite Muslim majority.
United States Secretary of State Hillary Clinton has condemned the use of force on both sides and called for the resumption of political dialogue.
Hospital sources say three policemen and at least two protesters were killed in the assault.
The military has imposed a curfew in several areas of the city.
The violence began a day after Bahrain declared martial law to quell sectarian unrest.
Troops from fellow Sunni-ruled neighbour, Saudi Arabia, were called in to help.
An MP from the largest Shi'ite Muslim opposition group has denounced the government assault as a declaration of war on the Shi'ite community.