Two civilians under contract with the NATO—led International Security Assistance Force (ISAF) were killed Monday in a suicide car bombing in Kabul, officials said.

The ISAF did not specify the location of the attack, but a NATO official said it took place in Kabul.

The nationalities of the contractors were not known.

The Afghan rebel group Hezb—e—Islami claimed responsibility for the suicide bombing, in which three Afghan civilians were also injured.

The incident took place near the Pul—e—Charkhi prison in eastern Kabul, which houses prominent insurgents and other detainees, police said.

Hezb—e—Islami is an Islamist militant group fighting foreign troops in Afghanistan. It is separate from the Taliban movement.

The organization’s political arm has put forward a candidate in the April 5 presidential election.

In December, a Taliban suicide attacker detonated explosives attached to a car near a NATO convoy in the same area of Kabul, killing three NATO personnel and injuring at least eight Afghan civilians.