A U.S. official says 13 American troops have been killed in the deadliest attack on coalition forces in Afghanistan in more than two months.

A suicide bomber rammed a van into an armored personnel carrier traveling in a NATO convoy. It happened as the convoy was passing the American University.

NATO and Afghan forces sealed off the area as fire trucks and ambulances rushed in. An Associated Press reporter at the scene saw two NATO helicopters landing to airlift casualties, while coalition troops using loudspeakers ordered bystanders to evacuate the area.

The Afghan Interior Ministry says three Afghan civilians and one policeman also died in the attack. Eight other Afghans, including two children, were wounded.

The Taliban claimed responsibility.

It's the deadliest single attack against the U.S.-led coalition since the Taliban shot down a NATO helicopter on Aug. 6 in eastern Afghanistan. That attack killed 30 U.S. troops, most of them Navy SEALs, and eight Afghans.