A roadside bomb struck a U.S. convoy in southern Afghanistan on Tuesday, killing three American troops, while a motorcycle bomb in a crowded village market killed at least three Afghan civilians, said officials.

NATO spokesman Col. Thomas Collins said the blast hit the American convoy in the Zhari district of Kandahar province, the spiritual heartland of the Taliban and one of the most volatile regions in Afghanistan.

The attack follows a truck bombing a day earlier on a NATO outpost in Helmand province that killed three Georgian soldiers.