Other sales have been blocked by U.S. authorities under the terms of the Missile Technology Control Regime, an informal international agreement between states designed to limit the spread of sophisticated long-range weapons technology.

General Atomics Aeronautical director of international strategy development Christopher Ames said on Wednesday the sale of armed drones to anyone other than the closest U.S. allies remained extremely unlikely.

But sales of the unarmed export Predator XP - specifically designed to be unable to carry lethal weaponry - were much more likely to be allowed and would soon start, he said.

"There has been very considerable international interest," he told Reuters in an interview on the company's stand at the Farnborough Airshow. "There have been countries that for a long time have been asking for Predator... (the export variant) opens up those markets to us."

At a cost of some $3 million to $4 million a drone, the export Predator is much cheaper than almost any manned aircraft capable of the same function, he said, costs less in fuel, and is often able to remain airborne for much longer.

The roughly $6 million maritime patrol Predator, he said, could perform many of the same tasks as a large maritime patrol aircraft with a crew of up to 10 and a pricetag of up to $200 million.

The San Diego-based privately owned company is one of the world's leading suppliers of drones, but is facing mounting competition as other aerospace firms - both U.S. and foreign - bring their own systems to market.

While General Atomics was not in a position to announce any sales during the show itself, he said the first deals would likely be announced in the coming months if not sooner. The total number of drones sold would likely be in the dozens, he said.