At least three drivers were injured in the incident early on Sunday, and Afghan officials were quick to blame Taliban fighters. But US military spokeswoman Lieutenant Cindy Moore said the blast, which sent plumes of black smoke billowing over Kandahar, was caused by "faulty fuel tanks".

She said military investigators determined that the blast originated inside one of the trucks, not outside.

"More than likely, it was some type of problem with the tank," she said.

The attack took place just after 3am on Sunday, while Pakistani and Afghan drivers were waiting to deliver fuel to the US base at Kandahar airport.

Tight security measures mean long waits for drivers delivering fuel to US bases in Afghanistan.