Despite a winter lull in fighting due to heavy snowfall in the mountains where the militant Taliban typically rest and regroup ahead of their annual spring offensive, roadside bombs continue to hit Afghan forces and their foreign allies.
A senior Afghan military official in Kandahar said the incident took place in the district of Dand when the device hit one of the armoured vehicles of the U.S. forces.
Foreign troops cordoned off the area and kept Afghan forces away from the scene, the official added.
The NATO spokesman said it was assessing the situation but declined to give details.
Taliban spokesman Qari Yousuf Ahmadi claimed responsibility for the attack and said the blast killed all the soldiers in the vehicle. The Taliban usually claim casualties and inflate figures when targeting Afghan and foreign troops.
Tens of thousands of Afghan civilians, members of the security forces and 2,400 U.S. military personnel have been killed in fighting since 2001, when the austere regime of the Taliban was toppled by US and coalition forces.