MANAMA, Bahrain – Troops and tanks locked down the capital of this tiny Gulf kingdom after riot police swinging clubs and firing tear gas smashed into demonstrators, many of them sleeping, in a pre-dawn assault Thursday that uprooted their protest camp demanding political change. Medical officials said four people were killed.

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

Foreign Minister Khalid Al Khalifa justified the crackdown as necessary because the demonstrators were "polarizing the country and" pushing it to the "brink of the sectarian abyss."