Afghan gunmen kill 2 U.S. troops

Updated at 10:28 a.m. ET

(CBS/AP) KABUL, Afghanistan - Two U.S. troops were shot dead in southern Afghanistan when three assailants, two of whom were believed to be Afghan soldiers, turned their weapons against American troops on Thursday.

Afghan and U.S. military officials confirm to CBS News that the dead were U.S. troops, and that a third American servicemember was wounded in the attack. U.S. forces responded with gunfire and killed the two assailants in Afghan army attire, wounding a third Afghan shooter in civilian clothing. The wounded shooter was identified as a teacher and is in custody.

CBS News correspondent Mandy Clark reports the shooting occurred inside a joint Afghan-U.S. base in Kandahar province.

Thursday's shooting is the latest case of Afghan policemen or soldiers -- or militants disguised in their uniforms -- killing NATO troops.

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Six Americans have now been killed and at least 15 wounded in attacks in Afghanistan since the Islamic holy books were burned at a U.S. base. Dozens of Afghans have been killed or wounded in riots.

Two U.S. military advisers were shot and killed Feb. 25 inside their office at the Afghan Interior Ministry. Days before that, an Afghan solider shot and killed two other U.S. troops during a protest over the burning of Korans at a U.S. base.

The U.S. says the Korans were burned with trash by mistake, and multiple American officials -- including President Obama -- have issued apologies.

On Wednesday, "CBS Evening News" anchor Scott Pelley spoke to U.S. Ambassador to Afghanistan Ryan Crocker and Marine Gen. John Allen, the commander in charge of the war.

"Clearly it's been a bad week," Crocker told CBS News, "but I'm quite confident we'll get through this. The pace of protest has slowed dramatically. A decade's worth of relationships doesn't go away in a single week, so we'll move forward."

Clark reports that, while the angry protests, which drew thousands of Afghans into the streets in the days after the Koran burning was made public, have died down, targeted attacks against U.S. forces by their supposed Afghan military partners seem to be on the rise.

While Crocker and Allen insist the U.S. mission continues unabated, Clark notes the prospect of increasing hostility from their partners in Afghanistan poses a serious challenge to U.S. troops, whose entire mission is pinned on the idea of living with and fighting with, not against, the Afghan security forces they're training.

In Thursday's shooting, Afghan and U.S. officials gave conflicting accounts about the sequence of events.

A district chief in southern Kandahar's Zhari district told The Associated Press the shootings took place on a NATO base when an Afghan civilian who taught a literacy course for Afghan soldiers and lived on the base started shooting at NATO troops. Niaz Mohammad Sarhadi said the shootings occurred at 3 a.m. and that NATO troops returned fire and killed the man and an Afghan soldier.

Mohammad Mohssan, an Afghan Army spokesman in Kandahar city, confirmed the incident occurred at a base in Zhari and involved two Afghans, one of whom was a soldier, who opened fire on coalition troops from a sentry tower. He said both were killed.

The shooting took place on the same day that Allen allowed a small number of foreign advisers to return to work at Afghan ministries after being locked down in secure locations.

Hundreds of advisers were pulled out of ministries and other government locations after the Interior Ministry killings. The Taliban claimed responsibility for the ministry shootings, saying they were conducted in retaliation for last week's Quran burnings, but no one has been arrested in the case.

U.S. military spokesman Lt. Col. Jimmie Cummings told The Associated Press Thursday that Allen approved the return of selected personnel. He did not elaborate which ministries were involved, but an Afghan official said some had returned to a department setting up a government-run security force that will guard international development projects.

A NATO official said less than a dozen advisers had returned. Both officials spoke on condition of anonymity because of the sensitivity of the issue.

NATO forces have advisers embedded in many Afghan ministries, both as trainers and to help manage the transition to Afghan control. The United States and international agencies also have hundreds of civilian advisers in ministries and on development projects run from coalition military bases around the country.

The program is the main component of NATO's exit strategy from Afghanistan and has so far cost the U.S. $22 billion in 2010 and 2011 to train and equip the Afghans.

This would be the beginning of a transition away from a combat role for U.S. and coalition forces, a process that U.S. Defense Secretary Leon Panetta has said may be completed as early as mid-2013.

After an Afghan soldier killed four French troops on Jan. 20, France reacted by halting its training program and threatening to withdraw its forces from Afghanistan earlier than planned.

Mr. Obama said Wednesday that his apology to Afghan President Hamid Karzai after U.S. forces mistakenly burned Muslim Korans had "calmed things down" but told ABC News that "we're not out of the woods yet." He said he apologized to assuage Afghan anger and protect U.S. forces.

Western officials, meanwhile, said a joint investigation by NATO and Afghan officials into the burnings was nearly complete, and preliminary findings could be released within days.