A U.S. Marine shot and killed an Afghan policeman after an argument Saturday in southern Afghanistan, NATO said. The military coalition said the two men had a dispute at a patrol base in Sangin, a volatile district of Helmand province. After the dispute, the Afghan policeman reportedly made threats and handled his weapon carelessly, NATO said. The Marine reported the behavior to his superiors, as AP reported. NATO said the Afghan policeman left his post but returned and pointed his gun at the Marine, who shouted at him to put the weapon down. When he didn't, the Marine fired two rounds, killing the Afghan policeman, NATO said. In the east, the coalition reported that a joint Afghan and NATO force killed several armed insurgents while tracking a Taliban operator in Nirkh district of Wardak province, west of Kabul. Eight militants were killed in the four-hour operation, which ended at 4 a.m. Saturday, according to the governor's office of Wardak province. Security forces recovered a machine gun, a rocket-propelled grenade launcher, several AK-47s and ammunition from the scene. Separately, a bicycle bomb targeting police vehicles near the center of the southern city of Kandahar wounded at least 10 people _ six civilians and four police _ said Kandahar Police chief Khan Mohammad Mujahid.