WASHINGTON, March 18, 2007 – U.S. military officials refuted a Taliban claim that they shot down a U.S. helicopter in Afghanistan’s Nuristan province on March 16. The claim is being made on an extremist Web site. U.S. forces have no reports of a downed aircraft and all coalition forces aircraft are accounted for, officials said. Also in Afghanistan, a United Nations mine-clearing worker was wounded by extremist small-arms fire during an ambush in Afghanistan’s Kapisa province yesterday, U.S. military officials reported. In the same incident, Afghan and coalition forces were also ambushed with rocket-propelled grenade, machine gun and small-arms...