At least 15 U.S.-led NATO soldiers, including 13 Americans, have been killed in two separate attacks in a single-day in Afghanistan, making it one of the deadliest days in 10 years of war of occupation.

Thirteen U.S. soldiers were killed in an attack against a convoy of American soldiers in the capital city of Kabul on Saturday, Press TV reported. 

A bomber detonated his explosives-laden car in the attack in Kabul's southwestern outskirts of Dar-ul-Aman where several government departments are located. 

The Taliban have claimed responsibility for the assault.

In another incident on Saturday, an Afghan soldier opened fire on foreign troops during training in Uruzgan Province. 

According to local officials, two Australian soldiers and their Afghan interpreter were killed in the shooting. Seven other people were also wounded. 

"We can confirm that 13 International Security Assistance Force members have died," said a spokesman for the NATO-led International Security Assistance Force (ISAF), Reuters reported.

Earlier, a spokesman for the Interior Ministry said three civilians and a police officer had been killed in the attack.

Excluding helicopter crashes, it was the deadliest single incident for foreign troops since the war began in 2001.

Lethal attacks are relatively rare in heavily guarded Kabul, compared with the south and east of Afghanistan, but Saturday's killings came less than two months after insurgents launched a 20-hour assault on the U.S. embassy in Kabul.

The assault on the International Security Assistance Force (ISAF) convoy took place in the Darulaman area in the west of the city, near the national museum.

The former royal palace, now in ruins, is also in the area, along with several government departments, and Afghan and foreign military bases.

The Taliban later claimed responsibility for the attack, saying they packed a four-wheel-drive vehicle with 700 kg of explosives.

Also on Saturday, three Australians and an Afghan linguist were killed in Uruzgan province in southern Afghanistan when an attacker wearing an Afghan National Army uniform opened fire on them, authorities in neighboring Kandahar province said.

Violence across Afghanistan is at its worst since the start of the war 10 years ago, according to the United Nations, despite the presence of more than 130,000 foreign troops.

ISAF says there has recently been a fall in attacks by insurgents but this data excludes attacks that kill only civilians and attacks on Afghan security forces operating without international troops.

On Thursday, insurgents armed with rifles and rocket-propelled grenades attacked two bases used by foreign troops in southern Afghanistan. An Afghan interpreter working for ISAF was killed in that attack, which stretched into Friday before the last of the four insurgents were killed.

There has been a series of high-profile assassinations, as well as day-to-day attacks by Taliban raiders, over the past year.

More than a dozen people were killed in the September attack on the U.S. embassy and ISAF headquarters.