The attack underscored the dangers faced by the NATO-led International Security Assistance Force (ISAF), even as they hand over much of the fighting to the Afghans ahead of a planned departure next year.
Nineteen US personnel have been killed in the last week in three air crashes and Saturday's bombing. Three British soldiers were also killed on Tuesday by a roadside bomb in the southern province of Helmand.
Maiwand borders Helmand province to the west and is considered one of the most volatile of Kandahar's districts.
Last month nine Afghan men working for a mine clearance organisation were taken captive by Taliban fighters there, though they were later released.