A grenade attack killed a US soldier in Iraq yesterday as a pipeline fire blazed on after an overnight explosion described by an Oil Ministry official as sabotage.

The US military said a second soldier was wounded in the attack on a military convoy at Khan Azad, some 20 kilometres south of Baghdad. The first was dead on arrival at hospital.

It was the latest in a spate of deadly assaults on US forces in which 19 soldiers have been killed since President George W. Bush declared major combat in Iraq over on May 1.

Two US soldiers were wounded in the town of Hit, about 140 kilometres northwest of Baghdad, on Saturday afternoon when their vehicle ran over a landmine.

About an hour before midnight, a US patrol reported a fire at an Iraqi fuel pipeline in the desert near Hit.

"This incident is an act of sabotage. The pipeline was blown up deliberately," said one Oil Ministry official. He did not elaborate and asked not to be named.

A Reuters correspondent at the scene said orange fireballs and thick black smoke were billowing from the damaged pipeline near a metal pylon more than 12 hours after the blast.

He said no US troops or Iraqi officials were on the spot and no attempt was being made to extinguish the blaze.

A US military spokesman said earlier that efforts were under way to put out the fire. He had no word on its cause.

It was the second major fire to damage Iraqi pipelines this month. US officials blamed the first on gas leaking from the main export pipeline from the Kirkuk oilfields to Turkey.

The oil pipeline at Hit, with a gas pipeline alongside it, was built in the 1980s to connect Iraq's southern and northern oilfields, enabling exports to flow smoothly.