NATO's International Security Assistance Force confirmed three casualties in a bombing in eastern Afghanistan but gave no details.

Afghan authorities said the attack happened in Wardak province, a hotbed of the Taliban insurgency just south of the capital Kabul.

Ataullah Khogyani, a spokesman for the provincial administration, told AFP that a suicide bomber riding a donkey blew himself up and killed three NATO soldiers and their Afghan interpreter.

Four Afghan soldiers who were also in the convoy in Sayedabad district were wounded.

There was no immediate claim of responsibility but the Taliban are behind almost all the suicide attacks in the country.

Along with roadside bombings, the suicide attacks -- often carried out by multiple insurgents storming buildings and government facilities in big cities -- are the group's main tactic.

Wardak is traversed by the highway between Kabul and southern and western provinces, including the key city of Kandahar in the south.