Radical students shouting "Drive out Yankees" firebombed a police bus Friday and wounded 13 officers in an attack on a U.S. government office in the southern city of Kwangju, police and U.S. officials said.

Two of the wounded officers were hurt seriously during the attack near the U.S. Information Service building in downtown Kwangju, the U.S. Embassy said in a statement. Police said four students were arrested.