The US military on Friday grounded all flights by its F-35 jets after a crack was found in the engine of one of the planes at Edwards Air Force Base in California, the Pentagon said.
Engineers sent the cracked engine part to manufacturer Pratt & Whitney for tests, dpa reported.
"It is too early to know the fleet-wide impact of the recent finding," the Defence Department said in a statement, noting it was working with the manufacturers of both the engine and the jet "to ensure the integrity of the engine, and to return the fleet safely to flight as soon as possible."
It was the second grounding of the aircraft in two months, following a suspension of F-35s flown by the Marines last month, the Army Times reported.
The fighter jet, made by Lockheed Martin, has been plagued by cost overruns and other problems. The military has 51 F-35s, which are used by the Navy, Air Force and the Marines.