A suicide car bomber killed two NATO civilian contractors in Kabul on Monday, the latest attack in the Afghan capital in the final year of the coalition's combat operations.

The blast near Kabul's main prison Pol-e-Charkhi in the eastern part of the city targeted a convoy of NATO troops, officials said.

NATO's International Security Assistance Force (ISAF), which has been waging a 12-year campaign against Taliban-led insurgents, did not give the nationality of the victims.

At around 2:30 pm (1000 GMT), "a suicide car bomber driving a (Toyota) Corolla car full of explosives rammed his vehicle into a foreign forces car in Pol-e-Charkhi area of Kabul", Hashmat Stanekzai, a Kabul police spokesman, told AFP.

Body parts and limbs of the suicide bomber were lying at the site of the attack, and at least three vehicles -- one belonging to the suicide bomber and two others cars -- were totally damaged.

The attack was claimed by Hezb-i-Islami, the second largest militant group in Afghanistan after the Taliban, in a phone call to AFP.

Warlord Gulbuddin Hekmatyar, the Hezb-i-Islami leader, vowed to kill as many Western soldiers as possible before the NATO pullout, in an interview last month with Britain's Daily Telegraph.

NATO and Afghan forces cordoned off the area after Monday's attack, which left three civilians wounded, according to the interior ministry.

"The ministry of interior strongly condemns this brutal attack by terrorists and prays for quick recovery of the wounded," a ministry statement said.

The Taliban and other Afghan insurgent groups have stepped up their attacks against Afghan and NATO troops, as international forces end their combat mission and withdraw from the country.

More than 50,000 NATO-led combat troops who are still in Afghanistan are due to leave by the end of the year.

The United Nations Assistance Mission in Afghanistan (UNAMA) warned Saturday of a new trend in the conflict in which more civilians were coming into the firing line as NATO forces reduced their operations.

UNAMA's annual report on civilian casualties recorded a 43 percent rise in the number killed and wounded in crossfire during ground battles in 2013.

The trend highlights the challenges faced by local forces as their better-equipped foreign partners leave and comes as Washington and Kabul squabble over a proposed security deal that would allow some US forces to stay on beyond 2014.

Washington is proposing that 5,000 to 10,000 US soldiers are deployed from 2015 to train and assist Afghan security forces in their battle against the Taliban militants.

But President Hamid Karzai has said that before he signs the so-called Bilateral Security Agreement (BSA), the US must stop military operations and bring the Taliban to the negotiating table.

Karzai, who has ruled the country since the fall of the Taliban in 2001, has suggested that a decision on whether to sign the BSA would fall to his successor, to be chosen in elections due on April 5.

Kabul was hit on January 24 by a devastating Taliban suicide attack on a Lebanese restaurant which killed 21 people, 13 of them foreigners.