All nine troops killed in a helicopter crash earlier this week - the worst for the coalition forces in four years - were Americans, the Pentagon confirmed, although it refused to provide further information on why the aircraft went down. NATO said there were no reports of enemy fire in a rugged area in the Daychopan district of Zabul province, where the crash took place on Tuesday. But Taliban spokesman Qari Yousef Ahmadi said that insurgents shot down the helicopter. The Taliban often exaggerate their claims and sometimes take credit for accidents. The US Defence Department released the identities of the troops late Wednesday, saying four were sailors and the rest were soldiers. Fort Campbell spokesman Rick Rzepka said that the five soldiers were assigned to the 101st Combat Aviation Brigade. Tuesday's crash was the deadliest since May 2006, when a Chinook helicopter went down while attempting a nighttime landing on a small mountaintop in eastern Kunar province, killing 10 US troops. Aircraft are used extensively in Afghanistan by both NATO and the Afghan government forces to transport and supply troops because the terrain is mountainous and roads are few and primitive. Lacking shoulder-fired missiles and other anti-aircraft weapons, the Taliban rely mostly on machine guns and rocket-propelled grenades to fire at aircraft during takeoffs and landings. Most helicopter crashes in the country have been accidents caused by maintenance problems or factors such as dust. On Wednesday, NATO said insurgents attacked a NATO and Afghan army outpost in eastern Afghanistan near the Pakistan border and at least 25 of the militants were killed in the resulting skirmish. Troops at the combat outpost in the Spera district of Khost province returned fire with mortars late Tuesday, killing 25 to 30 insurgents, NATO said in a statement. Initial reports found there were no civilian casualties, it said. Gen Raz Mohmmad Horya Khil, a senior commander of the Afghan National Army in the province, said 29 insurgents were killed. There were no casualties among NATO or Afghan troops, he said. Horya Khil said the attack, coming from the Pakistan side of the border, was directed at the Mir Safar joint-NATO and Afghan Army camp and lasted for more than two hours. Bodies and weapons on the field were being recovered, he said. Also on Wednesday, a NATO service member was killed by a homemade bomb in southern Afghanistan. NATO provided no further details, but the Danish military announced in Copenhagen that the bomb blast killed a Danish soldier and seriously wounded another. The two members of the Royal Life Guards were on foot patrol in Helmand province when the bomb went off, it said. Denmark has more than 700 troops serving in the NATO-led force. Most are based in Helmand province