Interior Ministry spokesman Dad Mohammed Rasa said 10 other civilians were wounded and an unspecified number of Canadian troops were hurt by the blast in the city of Kandahar.
U.S. military spokesman Lieutenant Colonel Jerry O'Hara confirmed there had been a bomb attack on a U.S.-led coalition convoy and said three soldiers were wounded. He declined to identify their nationality.
Taliban spokesman Qari Mohammad Yusuf claimed responsibility in a telephone call to Reuters.
Canada has about 650 troops in Afghanistan, most of them in Kandahar.