MANAMA, Bahrain—Riot police firing tear gas and rubber bullets stormed a public square occupied by antigovernment protests early Thursday in Bahrain, driving out demonstrators and killing at least two people, witnesses and hospital officials said, in a drastic turn in the protests swelling across the Arabian Peninsula and the broader Middle East.

Security forces in Manama, the capital of the tiny island kingdom, sealed off every entrance to Pearl Square, then entered the camp...