WASHINGTON (Reuters) - President Donald Trump said on Monday his administration had been able to cut some $600 million from the latest U.S. deal to buy about 90 F-35 Joint Strike Fighters, the Lockheed Martin aircraft the president has criticized for cost overruns.

Trump, speaking to reporters at the White House, said Lockheed Martin had been responsive to his concerns about the high cost of the stealthy, high-tech warplane.

“We cut approximately $600 million off the F-35 fighter, and that only amounts to 90 planes out of close to 3,000 planes,” Trump said, attributing that figure to Lockheed chief executive Marillyn Hewson.

Negotiations for the 10th batch of F-35 aircraft - about 90 planes - have been under way, with a deal expected by the end of the month. The contract was expected to be around $9 billion, with the price per plane falling below $100 million.

Trump said he became involved in the discussions over the cost of the aircraft about a month ago when he was still president-elect because the negotiations were not progressing.

“They were having a lot of difficulty. There was no movement. And I was able to get $600 million approximately off those planes. So I think that was a great achievement,” Trump said, suggesting the savings would be even larger as more planes are bought and as the administration looks at other contracts.

“We will be savings billions and billions and billions of dollars on contracts,” Trump said.

The United States is expected to spend some $391 billion over 15 years to buy about 2,443 F-35 aircraft, which are being built in different versions for the Air Force, Navy and Marines.

The price of the F-35 has typically been dropping with each new batch as Lockheed and the U.S. government ramp up production of the aircraft, which helps to lower overall costs.

While Trump and other U.S. officials have criticized the F-35 program for delays, cost overruns and high aircraft costs, the program has been stabilizing in recent years and the costs have been coming down.

“There were great delays, about seven years of delays, tremendous cost overruns,” Trump told reporters. “We’ve ended all of that and we’ve got that program really, really now in good shape, so I’m very proud of that.”