CAIRO—Egyptian security officials said Nobel Peace laureate Mohamed ElBaradei is under house arrest, the Associated Press reported, as tens of thousands of Egyptian antigovernment protesters clashed with police in Cairo.

Police were firing rubber bullets, tear gas and water cannons to disperse the protesters, including supporters of Mr. ElBaradei, which along with the prodemocracy leader had joined the latest wave of protests after Friday noon prayers. Police also used batons to beat some of Mr. ElBaradei’s supporters, who surrounded him to protect him. . .