A sixth worker was wounded in the ambush Monday in Kunar Province, said Abdul Jalal Jalal, the provincial police chief. The driver of the truck carrying the workers escaped unharmed.

Jalal said he suspected Taliban militants were behind the attack and that the labourers were targeted because they worked at an American base.

In Kabul, a roadside bomb exploded near a bus bringing Interior Ministry officials to work Tuesday, wounding one of them, said ministry spokesman Yousuf Stanezai.

Resurgent Taliban attacks have raised concerns about Afghanistan's shaky stability.

The United States said Monday it was giving Afghanistan $2 billion worth of military weapons and vehicles.