A Black Hawk helicopter has crashed in a restive corner of southern Afghanistan, killing seven US soldiers and four Afghans, the Nato-led coalition said.
A Taliban spokesman said they had downed the helicopter over southern Kandahar province, using a rocket-propelled grenade.
Although the group are quick to claim crashes caused by mechanical problems as successful hits by their fighters, they have brought down some Nato helicopters, including one two months ago in eastern Ghazni province.
In Kabul, Nato said only that it was investigating the cause of the crash and it was too early to say whether it was due to enemy fire or a fault with the aircraft.
It landed so hard that it was completely destroyed, Pentagon officials said. Everyone on board was killed, Nato said.
The helicopter, which was carrying US special operations troops, came down in insurgent-dominated Shah Wali Kot district to the north-east of Kandahar city, said Jawed Faisal, spokesman for the provincial governor.
Officials from the Nato-led International Security Assistance Force (ISAF) would not confirm the site of the crash, but said it was a volatile area and troops sent to recover the bodies and wreckage came under attack.
"About two hours after the crash we fought off a very minor assault, one or two individuals attacked with small arms fire. They were fought off by ISAF forces, who either killed them or drove them away," said spokesman Major Adam Wojack. "The current threat in the area is considered by ISAF as significant," he added.
Helicopter crashes have caused some of the highest death tolls of the war. Many have been the result of mechanical failures or errors by pilots flying in difficult conditions, but insurgents have brought down some aircraft.
Last August, the Taliban hit a Chinook with rocket-propelled grenades as it carried troops on a combat mission in eastern Afghanistan; the crash killed all 38 people inside.
It was the deadliest day of the decade-long war for the US military.
Many of those killed were from Navy Seal Team 6, the unit that killed Osama bin Laden in a night-time raid deep inside Pakistan, though it was not the same men on the chinook.
And in June, insurgents shot down a smaller helicopter in eastern Ghazni province, killing both officers on board.
Whatever its cause, the Black Hawk crash is the deadliest in Afghanistan since 12 March, when a Turkish helicopter hit a house on the outskirts of Kabul, killing 12 soldiers and two Afghan girls.
And it comes after a bloody week for foreign forces and Afghan civilians. There has been a string of insider attacks by Afghan police and soldiers on the Nato troops training them or fighting beside them, with six killed in two attacks last Friday.
On Tuesday, suicide attacks on a packed bazaar in south-western Nimroz province and a food market in northern Kunduz province killed 40 people and injured over 90 others, almost all of them civilians.
Mokhtar Amiri contributed to this story
