Updated at 1:40 p.m. ET
(CBS/AP) KABUL, Afghanistan - A man wearing an Afghan army uniform shot dead a U.S. service member in the east of the country, one of two NATO troops killed on Friday, military officials said. The Taliban took credit for the attack.
It was the 15th incident this year in which Afghan soldiers or insurgents disguised in military uniforms have turned their weapons on foreign troops. The shootings have increased the level of mistrust between the U.S.-led coalition and its Afghan partners and raised questions about the readiness of local forces to take over from NATO ahead of a 2014 deadline for the withdrawal of foreign combat troops.
An Afghan defense official said the incident took place in Kunar province in northeast Afghanistan. The official spoke on condition of anonymity because he was not authorized to brief the media.
NATO did not disclose the nationality of the trooper killed, but a Pentagon spokesman, Navy Capt. John Kirby, said the service member was an American.
Kirby said U.S. and allied officials are troubled that these attacks are continuing with some regularity despite efforts to improve the vetting of Afghans who are recruited into the army and police.
"It continues to be a very worrisome issue for us and for our Afghan partners," Kirby said.
The coalition said an investigation into Friday's attack was under way.
In a statement, Taliban spokesman Zabiullah Mujahid claimed the insurgent group was behind the shooting. The Taliban regularly take credit for attacks in the country, even if they were not involved.
The threat of Afghan soldiers or militants disguised in uniforms turning their guns on NATO troops has existed for years but has grown more deadly over the past five years.
(At left, watch David Martin's "CBS Evening News" report on the family of one U.S. soldier killed by a gunman in an Afghan police uniform)
While there were only a few deaths reported in 2007 and 2008, 35 foreign troops were killed in such attacks last year.
So far this year, there have been 15 such attacks, killing 20 NATO service members, Lt. Col. Jimmie Cummings, a spokesman for the U.S.-led NATO coalition, said Friday.
U.S. officials say that in most cases the rogue soldiers are motivated not by sympathy for the Taliban or on orders from the insurgents, but rather act as a result of personal grievances against the coalition.
NATO said a second service member died following an insurgent attack in southern Afghanistan, but did not provide further details about the death.