Seven American troops and four Afghans died in a Black Hawk helicopter crash on Thursday in southern Afghanistan, the NATO military coalition said. The Taliban claimed their fighters shot down the aircraft.

The crash marked another deadly day for the U.S. in Afghanistan, less than a week after six American service members were gunned down, apparently by two members of the Afghan security forces they were training to take over the fight against the insurgency as international combat troops prepare to exit the country by the end of 2014.

The spike in American deaths and attacks by Afghan allies have stirred fresh doubts about the prospects for the U.S. plan to leave a capable Afghan government in place when most troops depart after more than a decade of war.

Spokesman Brig. Gen Gunter Katz said the NATO coalition is investigating the cause of Thursday's crash in Kandahar province. The coalition had no immediate comment on the insurgents' claim that they shot down the helicopter.

Kandahar is a traditional Taliban stronghold and the spiritual birthplace of the hardline Islamist movement that ruled Afghanistan before being ousted in 2001 by the U.S.-led alliance for sheltering al-Qaida's terrorist leaders.

Among the dead were seven American service members, three members of Afghan security forces and one Afghan civilian interpreter, said Jamie Graybeal, a spokesman for the coalition. He said there were no survivors of the crash.

He declined to give any details on the mission of the helicopter, a UH-60 Black Hawk.

Taliban spokesman Qari Yousef Ahmadi said insurgent fighters shot down the helicopter in Kandahar province on Thursday morning.

"Nobody survived this," Ahmadi told The Associated Press by phone.

The helicopter was shot down in Kandahar's Shah Wali Kot district, which lies in the northern part of the province, said Ahmad Jawed Faisal, a spokesman for the provincial government said. He declined to give further details.

The area where the helicopter went down — a stretch of Kandahar along the border with Uruzgan province — is seen as a Taliban stronghold and key transit route. The insurgents regularly attack police checkpoints around the rural villages of the district and plant bombs in the road to catch passing government vehicles.

The Sikorsky UH-60 Black Hawk is a medium-lift helicopter that has served as the U.S. Army's workhorse since the 1980s.

The U.S.-led NATO force in Afghanistan has relied heavily on utility helicopters such as the Black Hawk to ferry troops, dignitaries and supplies around the mountainous terrain, thus avoiding the threat of ambushes and roadside bombs.

Thursday's crash is the deadliest since a Turkish helicopter crashed into a house near the Afghan capital, Kabul, on March 16, killing 12 Turkish soldiers on board and four Afghan civilians on the ground, officials said.

In August last year, insurgents shot down a Chinook helicopter, killing 30 American troops, mostly elite Navy SEALs, in Afghanistan's central Wardak province.

At least 221 American service members have been killed in Afghanistan so far this year.