An Afghan official says insurgents have ambushed a convoy of trucks in a restive province near the capital, Kabul, killing five members of a government guard force.

The spokesman for the governor of Wardak province says the convoy of supply trucks was being escorted by the Afghan Public Protection Force when it was ambushed on Tuesday on the country's main north-south highway in the Sayed Abad district.

Attaullah Khogyani says five guards were killed and one was wounded. He says the insurgents fled after the attack.

The highway is a key trade route for goods coming from Iran and Pakistan and headed for the capital.

Wardak is located next to Kabul and is considered a gateway and staging area for militant attacks there.