About 100 insurgents attacked and briefly occupied a government building in a town north of the capital early Saturday before U.S. troops and government forces drove them out, officials said. "Unknown gunmen attacked at dawn two police stations and the city hall. They occupied the city hall for a while," said Saad Ahmed Abbas, a municipal official in Al Khalis, 40 miles from Baghdad. Abbas said that U.S. soldiers and Iraqi security forces — including the police and national guard — regained control after a two-hour exchange of fire with the rebels. "Now the situation is calm," he said.A police officer said that about 100 rebels took part in the attack, and that they had left behind several mortars and rocket propelled grenades. Ghassan al-Khadran, deputy of governor of Diala province, said one policeman was injured in the shootout and that several rebels had been killed.