European planemaker Airbus, irked by accusations from rival Boeing that the design of its A350 jet remains in limbo, has hit back by saying its performance is guaranteed and predicting a boost at next week's Paris Air Show.

The A350 is the Airbus answer to the hot-selling Boeing 787 Dreamliner, due to be rolled out next month and enter service next year. The A350 went through numerous versions on the drawing board until Airbus launched the latest and, it says, final variant of the plane which is now dubbed the A350 XWB.

I have no idea because we don't know what this model will look like. Airbus still needs time to define exactly what its characteristics are. Right now it is between our 787 and 777."

Airbus chief Louis Gallois rejected this.

"It's wrong and I think it is completely unfair to say that," Gallois, who is also co-chief executive of parent EADS, said at a pre-air show briefing on Friday.

"I confirm that we are working full speed on development of the A350. We can guarantee performances to customers."

His comments were embargoed for release on Saturday.

Asked whether he expected fresh orders for the plane at the show, he said, "I think we will have good news on the A350."

Boeing is well ahead on orders after wrong-footing Airbus by developing its lightweight mid-sized airliner at a time when its European rival was focusing on the mammoth A380. Demand in the middle of the market is bigger than Airbus first thought.

Airbus responded last year with its revamped A350 XWB in three versions designed to carry 270 to 350 people on long routes.

It has 155 commitments including 13 firm orders for the new A350 but these are dwarfed by 584 firm orders for the 787.

While it denies having jitters over the basic design of the plane, Airbus acknowledges it is working on some of the plans and will not lock all details in place before October 2008.

The rival planes have also stirred up a row over technology.

Airbus is sticking with plans to make the A350 out of composite panels rather than barrel-shaped sections woven with modern fibres, a technique selected by Boeing for the 787.

ILFC, the world's largest aircraft lessor, whose purchasing decisions can make or break commercial aircraft ventures, has put pressure on Airbus to explain its choice of fuselage which Boeing describes as heavier and therefore less efficient.

Airbus says panels allow it to tailor each fuselage section to the forces which bear down on different parts of the plane.

Boeing and Airbus disagree over whether Airbus has a choice in terms of technology mastered by the European firm, however.

"Definitely we are sticking with (panels) and I shall meet (ILFC chief Steven Udvar-Hazy) in the next few days to try to convince him that our choice is economic and efficient," Gallois said.

ILFC is widely expected to order a batch of 787s at the Paris Air Show, or at least firm up orders which are already on Boeing's books but whose identity has not yet been disclosed.

The U.S. leasing giant gave broad approval to the redesigned A350 XWB, when it was introduced to the market last year but has so far said it wants to know more details about the plane, which is costing 10 billion euros to develop.