Image caption Different versions of the most advanced US fighter jet are flown by the navy and the marine corps

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.

Media playback is unsupported on your device Media caption Squadron Leader Steve Long of the UK's RAF explained the capabilities of the F-35 in 2010

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.