Washington, Feb 24 (IANS/RIA Novosti): All flight operations of Lockheed Martin F-35 Lightning II fighter planes have been suspended over an engine problem discovered on one aircraft, the US Department of Defense said.

According to the department, a routine engine inspection revealed a crack on an engine blade of the Pratt & Whitney F135 engine installed in F-35A aircraft operating at Edwards Air Force Base in California.

"As a precautionary measure, all F-35 flight operations have been suspended until the investigation is complete," the department said.

The suspension involves 17 aircraft undergoing testing and 34 in use for training in Florida and Arizona, and marks another setback for the Pentagon's most troubled and expensive weapons programme.

In January, the Pentagon grounded 25 F-35B planes, the Marine Corps variant with vertical take-off and landing (VTOL) capability, due to a manufacturing defect on an aircraft.

F-35s have been grounded before over electrical system problems.

The F-35 is currently still being tested, but low-rate initial production is already underway, with full-rate production due to begin around 2016.

The Pentagon wants to procure a total of 2,443 F-35s.

According to the latest Government Accountability Office report, the F-35's per unit cost has almost doubled since the inception of the Joint Strike Fighter programme in 2001.