US-led troops sealed off the road, often used by American soldiers travelling to the main US coalition base at Bagram outside the capital and also the route to various military bases on the outskirts of Kabul.

Attacks increasing

A US embassy spokesman said: "There was a vehicle-borne IED [improvised explosive device] that struck a US embassy convoy on Jalalabad Road.

"There were some injuries, including one seriously injured who has been evacuated for treatment."

The attack comes amid an increase in Taliban raids - including suicide attacks - in recent weeks as fighting increased after a lull over the winter.

NATO launched an offensive in the south last month.