The US has grounded its entire fleet of 51 F-35 fighter jets after the discovery of a cracked engine blade.
The fault was detected during a routine inspection of an air force version of the jet (F-35A) at Edwards Air Force Base in California, said the Pentagon.
Different versions are flown by the navy and the marine corps. All have been grounded.
The F-35 is the Pentagon's most expensive weapons programme. with a cost of nearly $400bn (£260bn).
The Pentagon said flight operations would remain suspended until the root cause is established.
Friday's order was the second time in two months planes from the F-35 range have been grounded.
The marine corps variant (F-35B), a short take-off and vertical landing variant (STOVL), was grounded for nearly a month after a manufacturing defect caused a fuel line to detach just before a training flight in January.
The air force version takes off from, and lands on, conventional runways while the STOVL version takes off from shorter runways and lands like a helicopter.
The UK is buying the STOVL variant for its future aircraft carriers.
It is replacing the scrapped Harrier jet which had a range of 300 nautical miles, compared with the F-35's 450 nautical miles.
With a top speed of 1,200mph (1,930km/h), the F-35 can fly almost twice as fast as the Harrier, while it also has radar transparency and stealth capabilities - the Harrier had neither.
