An engine fire last month on a US F-35 fighter jet was likely an isolated incident and not part of a wider problem for the new aircraft, a top Pentagon official said Thursday.

The comments came as Defense Secretary Chuck Hagel offered a ringing endorsement of the costly Joint Strike Fighter despite the latest technical setback that forced a halt of all F-35 flights.

The F-35 has been billed by manufacturer Lockheed Martin as a technological leap forward that will evade radar and fly at supersonic speeds.

Investigators have inspected the entire fleet of F-35 jets and have yet to pinpoint the cause of the June 23 fire that broke out on one plane during takeoff, said Frank Kendall, the Pentagon's top weapons buyer.

"There's a growing body of evidence that this may have been an individual situation, not a systemic one," Kendall told the House Armed Services Committee.

"But we don't know that for certain at this point in time," said Kendall, the undersecretary of defense for acquisition, technology and logistics.

At nearly $400 billion, the F-35 is the most expensive weapons program in US history and officials are anxious to reassure foreign partners and lawmakers that the warplane remains on track.

But the project has repeatedly faced technical glitches and the latest problem has turned into a public relations headache, just as the Pentagon planned to stage the plane's international debut at Britain's Farnborough air show starting next week.

US officers had to cancel the jet's participation in a British military aviation event on Friday in advance of the air show, an embarrassing result for both Washington and London. Britain was one of the first foreign governments to get behind the program, which now includes seven other countries.

US officials said no final decision had been taken on whether three of the aircraft would fly at the air show because engineers were assessing the potential safety risk.

At Eglin Air Force base in Florida, the site of last month's engine fire, Hagel told airmen Thursday he was pleased to hear glowing reviews of the hi-tech aircraft from the pilots who test-fly it.

"Some of the pilots told me it was the best aircraft that they'd ever flown, and some said it was the easiest and simplest aircraft they'd ever flown," he said.

"I was particularly happy to hear that because I believe this aircraft is the future for our fighter aircraft for our services."

Hagel acknowledged "issues" with the plane but said every new program faces technical hurdles.

He said that "I have strong, strong confidence" in the pilots and crews that fly and maintain the plane.

He added that safety would remain "the first priority."