The attack in Gereshk district happened on Sunday night, said the deputy police chief for Helmand province, Kamaluddin Khan.

Military supply convoys are regularly attacked in Afghanistan, where they are seen as an easier target for insurgents than NATO bases.

Separately, airstrikes by international coalition forces killed up to 14 suspected insurgents.

An airstrike in northern Baghlan province reportedly killed around 10 people on Sunday, a NATO statement said.

It had targeted a leader accused of planting bombs and supplying cash and weapons to Taliban leadership in the area.

However, NATO was not able to confirm the number of casualties because neither international or Afghan soldiers could get to the area.

Another airstrike in southern Nimroz province killed four fighters who were planting a bomb, said provincial police chief Abdul Jabar Pardeli.

A Taliban commander was among those killed by Sunday night's strike, he said.