"It was a suicide bombing carried out in a car right in front of Isaf (the Nato-led peacekeeping force)", Afghan defence ministry spokesman General Mohammad Zahir Azimi said, speaking from the scene.

Sirens blared as police and ambulances rushed to the area which was sealed off by international forces.

The attack comes ahead of presidential and provincial elections due on Thursday, which the Taliban have vowed to disrupt.

It is believed that a group affiliated to the Taliban is likely to be responsible for the attack.

In July 2008, a massive car bomb killed more than 50 Afghans and two diplomats outside the Indian embassy.