The U.S. has grounded its entire fleet of 51 F-35 fighter jets after the discovery of a cracked engine blade, BBC News reports 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, the Pentagon said.

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 program, with a cost of nearly $400bn.

The Pentagon said flight operations would remain suspended until the root cause is established. The 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.