He said the cargoes were 100,000 barrels and 200,000 barrels. Marine diesel is typically used to power assault craft, landing craft and a wide variety of war ships.

"They're also seeking two others to bring 225,000 barrels of jet each from the Far East to Diego Garcia early next month and from Greece to another Mediterranean location quite soon," he added. Diego Garcia in the Indian Ocean is the site of a U.S. Air Force base.

A fifth tanker would bring 340,000 barrels of jet fuel from the U.S. Gulf to the Mediterranean.

A similar cargo last month discharged in Spain, which made its air bases available to the U.S. for military operations in the wake of the attacks on New York and Washington.

But defence analysts said the bases were too far from the theatre of war to launch retaliatory strikes or even reconnaissance flights. "They're probably loading it onto aerial refuelling planes and moving it to other bases," said one.

A naval defence analyst said the marine diesel cargoes from the Mideast Gulf might be headed for Oman where British Royal Navy warships had recently been in port, or they could be discharged on to specialised naval transhipment tankers, which would supply the British and U.S. naval fleets.

Clifford Beal, editor of Jane's Defence Weekly warned against interpreting next month's jet loadings as signs of a sustained aerial bombardment of Afghanistan.

"The U.S. has other operations in the region," he said. "The U.S. Navy and Air Force routinely operate in the Gulf, Saudi and over Iraq. Some of this fuel will be the normal deployment."

The U.S. Department of Defense tendered last week for 64 million barrels of jet fuel for delivery at locations on the U.S. East Coast and Gulf Coast, with at least 32 million barrels due for delivery in the first year of the multi-year tender.