A Nato Black Hawk helicopter came down in southern Afghanistan on Thursday, killing seven American soldiers and four Afghans, the military said, as Taliban insurgents claimed to have shot it down.
The four Afghans included three members of the Afghan security forces and a civilian interpreter, Nato's US-led International Security Assistance Force (ISAF) said.
"The cause of the crash is under investigation," it said, adding that the helicopter was a UH-60 Black Hawk. The statement gave no further details.
Taliban spokesman Qari Yusuf Ahmadi told AFP: "Our mujahideen (holy warriors) shot down an ISAF helicopter in Chenarto area of Shah Wali Kot district in Kandahar province at around 11am (0630 GMT).
"The helicopter was destroyed and all the crew and soldiers inside the chopper were killed."
The ISAF statement did not use its normal phrasing for a simple helicopter crash, which includes the line that no enemy activity was reported in the area.
Helicopter crashes are fairly frequent in Afghanistan, where the 130,000-strong Nato mission relies heavily on air transport.
Last August, an American Chinook was shot down by the Taliban near Kabul, killing eight Afghans and 30 Americans, including 22 Navy SEALs from the same unit that killed Osama bin Laden in neighbouring Pakistan earlier that year.
It was the deadliest single incident for American troops in 10 years of war in Afghanistan.
On March 16, a Turkish helicopter crashed into a house on the outskirts of Kabul, killing 12 Turkish soldiers and two Afghan civilians.
Nato combat troops are scheduled to leave Afghanistan gradually and hand over responsibility for national security to Afghan forces by the end of 2014.