The Pentagon is close to confirming a $9bn (£7.3bn) deal with Lockheed Martin Corp for the sale of F-35 fighter jets, inside sources have revealed. Both sides are still negotiating the price of the planes, with the US Department of Defense poised to bring the price below $100m.

The contract would add another 90 jets to the US' arms program and is expected to be announced by the end of the month, according to three sources, who spoke to Reuters on the condition of anonymity. Lockheed has declined to comment on the deal but a representative for the fighter program said negotiations are ongoing.

President-elect Donald Trump has criticised the Pentagon's "out-of-control" F-35 program, while promising to bring down military expenditures once he takes office.

"We've been told through Lockheed that the president[-elect] has an ambition to reduce the cost of that aircraft by a material amount of money, many percent, into double digits over a period," Roger Carr, chairman of BAE Systems Plc, which is a key participant in the program told Bloomberg Television on 17 January.

Departing Defense Secretary Ash Carter has, however, defended the high-cost weapons program through which the DoD is expected to spend $391bn in the coming decades to develop and buy 2,443 of the supersonic warplanes, 200 of which have already been delivered.

"It's essential that it perform both in technology and in cost terms, and we've got to keep working on that," Carter said in an interview on Tuesday, pointing out that the program was critical to three U.S. military services and many allied air forces.

In an appraisal of the program, Carter acknowledged that it was "near collapse and disgrace" back in 2009 "because the development phase" was "grotesquely overrun in cost and behind in schedule". "We needed to instill discipline" and "eventually that was done" he explained.