A major U.S. leasing company has urged Boeing not to rush into developing a replacement for its 777 wide-body airliner, contrasting with pressure from some airlines to refresh its popular mini-jumbo.

Henri Courpron, chief executive of AIG subsidiary International Lease Finance Corp, said Boeing's hot-selling, 365-seat 777-300ER would work well for the industry into the next decade.

"The 777-300ER is working fine and does not have much competition. It is a formidable airplane. Why break that?" Courpron said in a telephone interview. "The market does not need a replacement any time soon."

He said Boeing in any case had its hands full resolving a crisis over the grounding of its 787 Dreamliner.

"I don't believe the 777 is the most urgent topic for the Boeing Company right now. They remain fully focused on resolving issues with the 787 and seeing it through the crisis," Courpron said.

Developed in the 1990s, the 777 mini-jumbo is seen as Boeing's most profitable plane. The timing of any replacement is one of the key decisions Boeing has to make in the coming year as it seeks to head off a challenge by European rival Airbus without sapping demand for its existing model.

Some international airlines such as Dubai's Emirates , the largest 777 customer with more than 100 in its fleet, want the new version soon in order to replace 777s coming up for retirement.

Emirates airline president Tim Clark said last week he thought Boeing would start offering the new aircraft to customers within weeks, targeting first delivery around 2020, which was later than his originally preferred date of 2017.

Delegates at this week's ISTAT aircraft trading conference in Florida, the biggest event in the industry's financial calendar, said Boeing would seek to end the grounding of its 787 Dreamliner first, then introduce a stretched version provisionally called 787-10X, and only then refresh the 777.

The proposal dubbed "777X" is not a completely new aircraft but will include a new wing and new engines. Industry sources say these may produce less power than the current General Electric powerplants, the world's largest commercial engines, because new materials will make the plane lighter and reduce the needed thrust.

However, the plane will not be as revolutionary as the 787 Dreamliner.

Courpron welcomed Boeing plans to offer the 787-10X.

"We think there is room for a regional wide-body (jet). It doesn't necessarily need the range Boeing is offering ... but we think the market will respond positively."

Airbus, meanwhile, is just months away from a maiden flight of its new A350 passenger jet designed to compete with the 787 Dreamliner, but a larger version seen as a challenge to the 777 so far exists only on paper. Courpron, whose company owns many 777s, said there was no urgency in reacting to the A350.

Airbus says its 350-seat A350-1000, designed with a lighter fuselage, will be more efficient for airlines to operate. Boeing is expected to counter that its 777X, with 400 seats, does enough to beat the A350 on economics by updating what is already a successful airliner.

(Reporting by Tim Hepher and Karen Jacobs; Editing by Alwyn Scott, Gary Hill and Dale Hudson)