FARNBOROUGH, England: Boeing has asked the U.S. government to seek greater transparency from the European Union over a three billion-euro (US$3.43 billion) loan package for Airbus, raising fresh concerns over aircraft subsidies despite an extended U.S.-EU truce on aerospace trade disputes.

In a letter to U.S. Trade Representative Jamieson Greer, Boeing said it was surprised by the European Investment Bank's June 29 announcement approving what it described as its largest-ever corporate loan to Airbus.

The company asked the U.S. Trade Representative to request a "full accounting of the terms of this loan" from the European Union and explain how it complies with the 2021 agreement, which called for an "open and transparent process."

Greer told CNBC that the USTR was examining the loan "very closely" and had discussed it with both the European Commission and Boeing.

"We can't accept a situation where companies don't have to operate under market-based systems, where Boeing has to operate and compete against an Airbus that gets unfair loans," Greer said. "If the European Union is giving unfair loans, then we need to take care of it and address it."

Boeing noted that the announcement, including an initial one billion-euro tranche, came four days after the European Union agreed to extend indefinitely a truce over tariffs linked to the long-running World Trade Organization dispute over aircraft subsidies.

"At a minimum, the timing of this loan is surprising," Boeing said in its letter.

The European Investment Bank said it finances thousands of companies every year and rejected suggestions that Airbus had received preferential treatment.

"This is a normal loan, carrying interest, part of the EIB's overall financing activity," a spokesperson said.

Airbus and Boeing declined to comment, while the USTR and the European Commission did not immediately respond to requests for comment.

The loan package is intended to support Airbus' long-term investments through 2030, the same year Airbus Chief Executive Guillaume Faury has said the company plans to begin developing a successor to the A320neo. Ahead of the Farnborough Airshow, Faury said the project is internally known as "eAction."

"The timing of this significant loan also coincides with Airbus leadership remarks publicly committing to a launch date of a new airplane, which further raises questions about both the size and the intent of this historic economic assistance package," Boeing said in its letter.

Boeing has said market conditions are not yet right for a new generation of aircraft, though analysts expect both Boeing and Airbus to begin new aircraft development by the middle of the decade.