Troops and tanks locked down the Bahraini capital of Manama on Thursday after riot police swinging clubs and firing tear gas smashed into demonstrators in a pre-dawn assault, killing at least four people.

Hours after the attack on Manama's main Pearl roundabout, the military announced a ban on gatherings, saying on state TV that it had "key parts" of the capital under its control.

Khalid bin Ahmed bin Mohammed Al Khalifa, Bahrain's foreign minister, justified the crackdown as necessary because the demonstrators were "polarising the country" and pushing it to the "brink of the sectarian abyss".

Speaking after meeting his Gulf counterparts, he said the violence was "regrettable". Two people had died in police firing on the protesters prior to Thursday's deadly police raid.

An Al Jazeera correspondent, who cannot be named for security reasons, went to Salmaniya hospital, which was thrown into chaos by a stream of wounded protesters from the violence at the Pearl roundabout.