Delta Air Lines confirmed Monday it was in negotiations to buy new aircraft, but declined to comment on a report that it was planning to buy 100 Boeing 737 planes.

The board of the Atlanta, Georgia-based airline will vote on an order for the 737-900ER extended-range jets, in a deal with a list price of about US$8.58 billion, later this week, Bloomberg news agency reported, citing two people familiar with the matter.

"Delta does not currently have any information to release regarding new aircraft," a company spokesman said in an email to AFP.

"As previously announced, Delta has been holding discussions with major manufacturers on a long-term plan to replace older aircraft, in order to maintain a flexible, cost-efficient fleet that meets our customers' needs in the years to come," spokesman Trebor Banstetter said.

Boeing does not comment on negotiations with its customers, Boeing spokesman Doug Alder told AFP.

"We're always working to try to find the best solutions for what... different airlines looking for," he said. "When something is in negotiation, we just don't comment on it."

Delta, based in Atlanta, Georgia, is the world's largest airline in terms of passengers carried, according to the International Air Transport Association.

Its global network serves 353 destinations in 64 countries on six continents, with a fleet of more than 700 aircraft, according to the firm.

In January, Delta said in an internal memo that it was moving to replace 200 aging aircraft.

The U.S. airline has approached manufacturers with a view to buying "100 to 200 firm aircraft" with an "option for 200 more" from early 2013, according to the memo posted on Delta's intranet.

The memo did not name the companies approached.