U.S. officials confirmed with local media that 13 NATO soldiers killed in an Afghan bombing Saturday were Americans, the biggest single day loss to U.S. troops there since the August crash of a helicopter that killed 30 U.S. soldiers.

CNN quoted anonymous U.S. military officials as saying the bombing, carried out by a suicide bomber in a van, targeted an armored NATO bus on a highway in the Afghan capital Kabul.

Afghan Interior Ministry said an International Security Assistance Force (ISAF) convoy was attacked on Darul Aman road in western Kabul at around noon. In addition to 13 ISAF casualties, three Afghan civilians and a policeman were also killed.

In August, 30 U.S. servicemen were killed aboard a Chinook helicopter in central Afghanistan when it was downed by a Taliban rocket. Seven Afghan commandos and an Afghan interpreter also were killed.