PHOENIX: Airbus is seeking airline support for a new 400-seat jetliner provisionally dubbed the A350-8000 as competition escalates with Boeing over the world's largest two-engined jets, airline and aviation industry sources said.

After talking up the possibility of a new member of its A350 family, the European planemaker has swung into an active pre-marketing phase as it responds to a recent upgrade in the competing Boeing 777.

While Boeing has scored successes in the Gulf with its biggest-ever twin-engined jet, the 406-seat 777-9, Airbus is expected to aim its design at airlines that do not always require the performance needed for extreme Gulf conditions.

"It would have similar capacity and range (as the 777-9) and substantially lower seat-mile costs," Airbus sales chief John Leahy said in an interview on the sidelines of the Istat Americas air finance conference.

"We are showing it to airlines right now."

The project is the latest move in a game of leapfrog played by Airbus and Boeing over the past decade in the market for big twinjets, valued at about $1.9 trillion over 20 years.

It marks a shift in priorities after the oil price collapse eased pressure on Airbus to upgrade its larger four-engined A380, the output of which is declining because of slow sales.

Two airlines whose stance could be decisive in whether Airbus launches the new jet are Singapore Airlines and British Airways.

Singapore took delivery of its first smaller A350-900 model this week and has long been weighing up the 777-9.

Both airlines declined to comment.

In Singapore, where Airbus' planemaking president, Fabrice Bregier, stopped over on Thursday after a China visit, a company spokesman declined to comment.

The A350 XWB (Extra Wide Body) family was launched after a string of setbacks in 2006 to compete with Boeing's mid-sized 787 Dreamliner and the larger 777.

Boeing responded to the all-new jet by upgrading its existing 777 family to include the 777-9, one of a pair of jets also known as the 777X series.

Boeing has sold 306 777X jets. But after an initial burst, sales have hit a lean patch. Airbus has sold 181 A350-1000s.