At least 14 people, mostly foreign forces, were killed when a Taliban car bomber struck a US-run NATO convoy travelling through the Afghan capital Kabul on Saturday.

The attacker detonated his Toyota Sedan car at 11:20 am (0650 GMT) in the southwest of the city, and at least ten foreign forces, three civilians and a policeman were among the casualties, police and Western officials said.

"The attack targeted an American NATO bus," said a Western military official on condition of anonymity. "There are 10 or 11 people, mostly Americans," he said, giving the foreign death toll.

Spokesman for the interior ministry Siddiq Siddiqui said that three Afghan civilians and a policeman had been killed but he had no information on foreign casualties.

"It was a huge explosion, I saw at least ten bodies of foreign forces taken out of their capsized bus and evacuated by two helicopters," one witness told AFP at the scene.

Thick black smoke could be seen rising from a fire still burning at the scene, while fire hoses were putting out another nearby, footage on private television channel Tolo showed.

NATO's coalition forces were seen tending to at least once casualty on the ground, while fire trucks and ambulances, sirens blaring, were on their way to the scene where one charred vehicle could be seen lying on its side.

At Kabul's Estiqlal hospital, ten people had been brought in for treatment, but one policeman and one woman had since died of their injuries, said the head of the hospital Mohammad Ali Eshan.

One of the injured, 30-year-old Abdullah, who like many Afghans goes by just one name, had hurt his hands and face in the attack.

"I was driving my motorcycle, a convoy of foreign forces had stopped around 100 metres away. I suddenly heard a loud explosion and was knocked down," he said. "When I opened my eyes I was in hospital."

A spokesman for NATO's International Security Assistance Force (ISAF) confirmed the attack.

He said "several" Afghans and coalition forces had been hurt, but refused to give the nationalities of the service members, in line with ISAF policy.

"A vehicle-born improvised explosive device detonated today in Kabul, causing a number of casualties and severely damaging an International Security Assistance Force vehicle," the alliance force said in a statement.

"Initial reports indicate several ISAF service members and local Afghan casualties."

The Taliban, fighting Afghan and Western forces to regain control of Afghanistan after ten years of bloody insurgency, claimed responsibility for the attack.

"A suicide car bomb attack was carried out on a bus of foreign forces in the Dar-ul-Aman area of Kabul," said Taliban spokesman Zabiullah Mujahid in a text message sent to AFP.

At around the same time in the eastern city of Asadabad in Kunar province, a female suicide bomber blew herself up outside a local branch of Afghanistan's spy agency, a spokesman for the Kunar provincial governor said.

The woman struck outside the local operations centre for the National Directorate of Security (NDS), said spokesman Wasifullah Wasifi.

"As a result of the explosion two guards of the operative directorate were wounded," he said.

Also on Saturday, two NATO troops were killed when a man dressed in an Afghan army uniform turned his gun on them, the coalition said, adding that the shooter was later killed.

The attacks come a day after the Taliban launched a four-hour long assault on a US-run civilian-military base and NDS local branch in the southern city of Kandahar, the spiritual birthplace of the insurgent movement.

Earlier in the week it was announced in Kabul that Afghan President Hamid Karzai would next week give a list of areas in up to 17 provinces that will soon see a handover from NATO to Afghan control as Western governments begin to bring troops home with the overall combat mission due to end in 2014.

A regional conference is to be held in Istanbul next week as international backers of Karzai's government push talks with the Taliban aimed at finding peaceable resolution to the long war.