Two people have been killed after a convoy of foreign military vehicles was targeted in an explosion at a prison in eastern Kabul, sources have told Al Jazeera.

A police chief told Al Jazeera that the bomber targeted two vehicles on Monday near the Pul-i-Charkhi prison on the Kabul-Jalalabad highway. 

NATO's International Security Assistance Force (ISAF), did not give the nationality of the victims - who were NATO civilian contractors.

Hezb-e Islami, which is allied with the Taliban, later claimed responsibility for the attack. 

In an interview with Britain's Daily Telegraph newspaper last month, Gulbuddin Hekmatyar, the leader of the group, vowed to kill as many Western soldiers as possible before the NATO pullout.

A local shopkeeper named Jameel, told the Associated Press news agency that he saw two NATO vehicles leaving the prison when a car slammed into the second one. There was no immediate word on casualties.

Police and ambulances went to the scene near the prison where two civilian vehicles lay overturned and nearby shop windows were shattered from the force of the explosion.

Armed rebels have stepped up attacks in the final year of the international coalition's combat mission in Afghanistan, seeking to shake confidence in the Kabul government's ability to keep order.

Afghanistan's Ministry of Interior strongly condemned the attack in a statement released on Monday.

Source: Al Jazeera and agencies