KABUL (Reuters) - NATO troops tried to ascertain on Sunday if Taliban insurgents had shot down a troop-carrying helicopter in Afghanistan, killing 38 people in the largest loss of life suffered by foreign troops in a single incident in 10 years of war.

In what has proved to be a bloody two days for foreign forces in Afghanistan, another two unidentified NATO troops were killed in two separate attacks by insurgents in Afghanistan's violent east and south, the coalition said.

Thirty U.S. soldiers -- some from the Navy's special forces SEAL Team 6, the unit that killed al Qaeda leader Osama bin Laden -- seven Afghans and an interpreter died in Friday night's crash which came just two weeks after foreign troops began a security handover to Afghan forces.

The Taliban quickly claimed responsibility for bringing down the helicopter with a rocket-propelled grenade. Although it often exaggerates incidents involving foreign troops, a U.S. official in Washington said the helicopter was believed to have been shot down.

The NATO-led International Security Assistance Force (ISAF) in Afghanistan confirmed the death toll overnight, which was first announced by Afghan President Hamid Karzai, and said the cause of the crash was still being investigated.

ISAF officials in Kabul remained tight-lipped on Sunday about possible causes of the crash and said the process of recovering the bodies from the crash site in a valley about 80 km southwest of the capital was still going on.

The deadly crash comes at a time of growing unease about the increasingly unpopular and costly war. Foreign forces are due to complete their security handover to Afghan troops and police by the end of 2014.


The CH-47 Chinook crashed in central Maidan Wardak province in a hard-to-reach valley surrounded by rugged mountains.

Despite its proximity to the capital, the area is one of the most dangerous in central Afghanistan, with fighters from the Taliban, the al Qaeda-linked Haqqani network and other militant groups all active there.

"No words describe the sorrow we feel in the wake of this tragic loss," General John Allen, who took over from General David Petraeus three weeks ago as commander of all foreign troops in Afghanistan, said in a statement released overnight.

"All of those killed in this operation were true heroes who had already given so much in the defense of freedom."

A U.S. official said some of the dead Americans were members of SEAL Team 6. None of the dead had been part of the bin Laden raid in Pakistan in May.

The crash was the deadliest single incident for U.S. troops in Afghanistan since the Taliban were toppled by U.S.-backed Afghan forces in late 2001, ISAF said.


U.S. Defense Secretary Leon Panetta said in a statement on Saturday that the United States would "stay the course" to complete the mission in Afghanistan, a sentiment echoed by NATO Secretary General Anders Fogh Rasmussen.

The crash will likely raise more questions about the security transition and how much longer troops should stay. All foreign combat troops are due to leave by the end of 2014, but some U.S. lawmakers question whether that is fast enough.

"While acknowledging the immense personal tragedy of the loss of life in this helicopter disaster it is even more important to acknowledge that a greater tragedy would be to buckle under an understandable wave of emotion, and use it as a reason to withdraw now," wrote former British chief of the general staff General Lord Dannatt in The Sunday Telegraph.

Karzai "shared his deep sorrow and sadness" with his U.S. counterpart, Barack Obama, and the families of the victims.

With doubts lingering about the cause of the crash, Karzai met his security advisers on Sunday to discuss what he called the "helicopter incident." He warned them to be on guard for more attempts by insurgents to derail the transition process.

"As there is the transition process going on, enemies of Afghanistan want to disrupt the national process by any means," Karzai said in a statement released by the presidential palace.

U.S. and other NATO commanders have claimed success in reversing a growing insurgency in the Taliban's southern heartland, although insurgents have demonstrated an ability to adapt their tactics and mount attacks in other areas.

But violence is at its worst in Afghanistan since U.S.-backed Afghan forces toppled the Taliban government, with high levels of foreign troop deaths, and record civilian casualties during the first six months of 2011.

Last year was the deadliest of the war for foreign troops in Afghanistan with 711 killed. The crash in Maidan Wardak means at least 375 foreign troops have been killed so far in 2011. More than two-thirds were American, according to independent monitor www.icasualties.com and Reuters figures.

(Additional reporting by Mirwais Harooni; Editing by Paul Tait and Jonathan Thatcher)

mochila insert follows