(CNN) -- The Taliban claimed responsibility Friday for downing a Black Hawk helicopter in southern Afghanistan.
"Yesterday (Thursday) evening Taliban fighters shot down a helicopter and killed all its passengers in Khanashen Dewalak area near Garmsir, southern Helmand province," a Taliban spokesman wrote to CNN.
The helicopter's four crew members, all of them American, are believed to be dead, a U.S. military official said.
The copter was flying in bad weather, the official said Thursday. "We cannot yet rule out enemy action," the official said.
Fatal helicopter crashes involving members of the NATO-led International Security Assistance Force are not unprecedented in Afghanistan, with some of the aircraft brought down by enemy fire while others crashed for mechanical reasons.
The single deadliest loss for U.S. troops since the Afghan war began in late 2001 happened in August when 30 U.S. service members died as a helicopter carrying them went down while they were reinforcing other troops, officials said. Seven Afghan troops died in that same crash.
A U.S. military official said then that insurgents were believed to have shot down the CH-47 Chinook. The Taliban claimed that militants downed the helicopter with a rocket-propelled grenade.
Last month, 12 people died when a helicopter crashed in Afghanistan's capital of Kabul. There was no reported "insurgent activity in the area" at the time, said Capt. David Yaryar, a spokesman for the NATO-led force.