The Pentagon reduced Sunday the number of Americans killed in a Taliban car bomb attack the day before on a NATO convoy in Kabul from 13 to 10 after British and Canadian casualties were reported.

"There were five ISAF (International Security Assistance Force) service members killed, of which four were US," a defense official in Washington told AFP, speaking on condition of anonymity.

"Eight civilian employees were also killed, of which six were American. I cannot confirm other nationalities," the official said.

The Foreign Office in London earlier Sunday said two British contractors were among the 13 foreigners who died alongside four Afghans in one of the bloodiest attacks of the decade-long Taliban insurgency.

Canada's military said a Canadian soldier was also among the dead.

US defense officials told AFP on Saturday that all 13 foreigners killed were American.

At least 17 dead in attack on US convoy in Kabul
Kabul (AFP) Oct 29, 2011 - A Taliban car bomber struck a NATO convoy in the Afghan capital on Saturday, killing at least 17 people, including 13 Americans, in one of the deadliest attacks to hit foreign forces in more than a decade of war.

The attacker blew up his Toyota sedan next to a US-run military bus travelling through the southwest of Kabul next to the Dar-ul-Aman palace ruins at 11:20 am (0650 GMT), in the latest in a spate of high-profile attacks.

The bombing was one of three deadly incidents for alliance forces in a day and came as NATO prepares for a second wave of transition to local forces, and ahead of two upcoming international conferences aimed at bridging peace.

The interior ministry said three bystanders and a policeman were killed, while NATO's alliance force said at least 13 foreigners died -- five troops and eight civilian employees, who US officials confirmed were all American.

At least one other soldier was wounded in the massive explosion, US officials told AFP, warning that the death toll could rise.

A Canadian soldier was also among the dead, the Canadian military said later, but it was not immediately clear whether his death added to the toll.

Thick smoke rose from a fire that raged long after the explosion, which was on a main road. The scene was cordoned off by Afghan and ISAF forces who were seen carrying the charred bodies of the dead on stretchers away from the whitened bus wreckage.

Half a kilometre from the explosion, shattered windows and scattered pieces of twisted metal showed the scale of the blast.

"It was a huge explosion, I saw at least 10 bodies of foreign forces taken out of their capsized bus and evacuated by two helicopters," one witness told AFP at the scene.

President Hamid Karzai and top US commander in Afghanistan General John Allen condemned the attack. The US Embassy in Kabul offered its deepest condolences to the families and friends of those killed.

The attack was the deadliest for the coalition since the death of 30 US troops, including 25 US Special Operations Forces, whose helicopter was shot down in mid-August south of Kabul in Wardak province.

Over the past few months a series of attacks in the capital have shown the resilience of the Taliban, more than ten years after the Islamist movement was toppled from power by a US-led invasion.

Eight other major incidents have hit Kabul since the beginning of the year, including a complex attack on a luxury hotel that killed 21 people in June, a deadly suicide bombing on a British cultural centre and a siege of the US embassy and NATO headquarters that killed at least 14 in a 19-hour siege.

The assassination last month of the government's chief peace broker, former president Burhanuddin Rabbani, also in Kabul, underscored the vulnerability of the capital as Kabul's Western backers push for solutions to end the war and remove their combat troops by the end of 2014.

A regional conference is to be held in Istanbul next week at which President Hamid Karzai is to give a list of areas in up to 17 provinces that will soon see a handover from NATO to Afghan control.

But there are deep doubts over the ability of the fledgling Afghan army and police to secure the country, with the Taliban proving their ability to strike in the once-peaceful north that was once a bastion of resistance to the rebels.

In the volatile southern province of Uruzgan also Saturday, three Australian army trainers were killed when an Afghan soldier turned his gun on them, NATO and Afghan army officials said.

And 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, wounding two guards, a spokesman for the Kunar provincial governor said.

The insurgent group claimed responsibility for the attacks in Kabul and Kunar.

"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 Kabul's Estiqlal hospital, 10 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."

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.