WASHINGTON (AFP) - Boeing is moving forward on launching the new version of its long-range 777 jetliner in talks with customers, company officials said on Thursday.

"We are taking the next step when it comes to engaging customers on the 777X," said Mr Doug Alder, spokesman for Boeing's Commercial Airplanes unit, referring to the new version dubbed 777X.

"We've made great progress in our development work and have begun to discuss additional technical, pricing and schedule details with customers," he said in an email to AFP.

Mr Alder declined to comment on reports that Boeing's board of directors on Monday had approved the start of selling the new version of its popular twin-aisle jetliner, which dominates the long-haul market.

The reports, including by The Wall Street Journal, cited anonymous sources.

Boeing spokesman Karen Crabtree told AFP that the company had been working closely with airline and leasing customers to develop options "for improving on the 777's popularity".

Boeing continued to target the 777X's entry into service near the end of the decade, she said.

"We are aggressively moving forward per our plan and customers are happy with our progress," the spokesman added.

The timing of a decision to launch the program will depend on market response during this "next phase" of discussions about the airplane, she said.

"We are confident that, when the market demands it, we will develop and deliver a superior airplane that ensures the 777 remains the unequivocal long-haul leader."

The 777, which entered service in 1995, can transport up to 500 passengers in single class in its 777-300 model.

Ms Crabtree said the 777X will be "the world's largest and most efficient twin-engine airplane."

The 777X faces competition from Boeing's European arch-rival Airbus, whose new A350, a twin-engine long-haul jetliner, is expected to enter service in the second half of 2014.

Dow member Boeing's shares were up 1.2 per cent in afternoon trade on the New York Stock Exchange.