The Kabul incident happened close to a school on a main road linking the US embassy to the city's airport.
The attack against foreign troops occurred in the southern city of Kandahar, witnesses said. There were no immediate reports of any casualties, they said. Troops had sealed off the site of the suspected suicide blast, they said.
Nearly 200 people have been killed in suicide attacks in Afghanistan this year, most of them civilians.

Copyright Reuters, 2006