At least 14 people, including 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 the area was now blocked by Afghan and international forces, said police spokesman Hashmat Stanikzai.
At least ten foreign forces, three civilians and a policeman were among the casualties.
"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 death toll.
Spokesman for the interior ministry Siddiq Siddiqui said that three civilians and a policeman had also been killed but he had no information on foreign forces.
"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 an inferno 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 one 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.
A spokesman for NATO's International Security Assistance Force (ISAF) said the force could not give further details until further information had been gathered.
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.
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.