KABUL (AP) — Insurgents shot down a U.S. helicopter after exchanging fire with its crew in central Afghanistan on Monday, while a suicide bomber in the north killed two U.S. soldiers inside a police station, officials said. The helicopter was forced down in Wardak, one province west of Kabul, after insurgents hit it with gunfire Monday, said Lt. Cmdr. Walter Matthew, a U.S. military spokesman. The crew survived and have been extracted from the area, he said.”The helicopter crew exchanged fire with the enemy before the damage brought the helicopter down,” Matthews said.