Prayers for their families.

KABUL, Afghanistan (CBS/AP) — A U.S. official said all 13 NATO service members killed in a suicide bombing in the Afghan capital were American troops.

The car bomb struck an American convoy in Kabul, hitting an armored bus carrying U.S. soldiers which then burst into flames.

The official confirmed the nationalities shortly after NATO issued a statement saying that 13 of its forces were killed in Saturday’s blast. The official spoke on condition of anonymity because of the sensitivity of the issue.

The attack also killed four Afghan civilians, including a policeman and schoolchildren

CBS News correspondent Mandy Clark, reporting from Kabul, said helicopters landed near the scene and air-lifted a number of casualties, according to eyewitnesses.

“It was a huge blast,” one eyewitness said. “I went closer to the convoy and saw several Americans on fire.”

The Taliban claimed responsibility for the attack. They said the bomber had more than 1,500 pounds of explosives in his car.