A suicide car bomb targeting foreign troops in the Afghan capital on Thursday killed six civilians, Kabul's police chief said.

"Six civilians were martyred and 18 other civilians were wounded in the suicide car bomb attack against coalition forces," General Salim Ahsas said.

Ahsas told reporters the blast did not harm America-led troops who were travelling on the road to Kabul's international airport when the bomb exploded.

The blast took place during morning rush hour on one of the city's busiest roads.

The force of the blast damaged about 10 cars, General Ali Shah Paktiawal, head of the police criminal investigation branch said.

The wounded were rushed to different hospitals in the city, he added.

Two armoured vehicles -- apparently the target of the attack -- were also damaged.