All the tankers were destroyed in Friday's blast and clouds of black smoke poured over the Kandahar airfield, the main base for the US-led forces in southern Afghanistan, before the fires were extinguished.

Afghan army commander General Mohammed Sarwar said a bomb was believed to have been hidden in one of the tankers. He said the two injured drivers had been taken to a hospital.

US military spokeswoman Sergeant Marina Evans confirmed that some fuel tankers had been hit by a blast and had caught alight, but said the tankers belonged to the Afghan army and had been driving past the base when one hit a landmine.

However, an Associated Press reporter saw the blackened remains of the eight tankers in one of the base's parking lots, next to its outer walls.

String of attacks

There has been a string of attacks on tankers contracted by the US-led forces to haul fuel to its bases from neighbouring Pakistan. Friday's was the biggest in months.

The blast came amid a major surge in violence by Taliban-led rebels that has left more than 1400 people dead in the past half year and raised fears for Afghanistan's nascent democracy.

Violence has risen sharply in and around Kandahar, a former Taliban stronghold, with four bombings in recent weeks and five medical aid workers killed on Wednesday as they were returning to the city after treating people at a nearby refugee camp.