It was the second grounding of the warplane in two months.

The F-35 program office said it was too early to know if this was a fleet-wide issue, but it was suspending all flights until an investigation was completed.

It said it was working closely with Pratt & Whitney, the United Technologies Corp unit that builds the engine, and Lockheed Martin Corp, the prime contractor for the radar-evading warplane, to ensure the integrity of the engine and return the F-35 fleet to flight as soon as possible.

The Pentagon's F-35 program office began notifying the chiefs of the US Air Force, Navy and Marine Corps late on Thursday about the engine issue and decision to ground the planes, said Kyra Hawn, a spokeswoman for the Pentagon's F-35 program office.

She said that during a routine inspection at Edwards Air Force Base in California on Feb. 19 inspectors found a crack on a low pressure turbine blade that is part of the F-35's F135 engine. The blade was on F-35 A-model, or Air Force variant, which takes off and lands from conventional runways.

Engineering teams would remove the blade and ship it to Pratt's engine facility in Middletown, Connecticut, for more thorough evaluation and root cause analysis. An initial analysis was expected next week, she said.

The grounding comes on the heels of a nearly month-long grounding of the Marine Corps variant of the new warplane after a manufacturing defect caused a fuel line to detach just before a training flight in Florida.

The Marine Corps variant of the F-35, which takes off from shorter runways and lands like a helicopter, was grounded for nearly a month after a fuel line detached just before a training flight at Eglin Air Force Base in January.

That issue was later found to be caused by a manufacturing defect. The Pentagon and the US Navy lifted flight restrictions on the B-model of the plane on Feb. 13.