KABUL, Afghanistan — A Taliban suicide bomber rammed a van into an armored NATO bus Saturday in Kabul, killing 13 American troops and four Afghans, U.S. and Afghan officials said.

It was the deadliest attack on coalition forces in more than two months.

The explosion, which occurred as the convoy was passing the American University, sparked a fireball and littered the street with shrapnel. Heavy black smoke poured from burning wreckage at the site.

The armored personnel carrier, known as a Rhino, was sandwiched between a convoy of mine-resistant military vehicles traveling on a four-lane highway frequently used by NATO forces in a southwestern section of the city.

NATO said 13 service members were killed, but a U.S. official confirmed they were all Americans.

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