The Pentagon on Friday grounded the entire fleet of F-35 fighter jets, after discovering a crack in one of the multi-million-dollar plane's engine blade.

The problem was discovered during a routine engine inspection at Edwards Air Force Base, California, of an F-35A, the Air Force version of the fighter jets.

"As a precautionary measure, all F-35 flight operations have been suspended until the investigation is complete," the statement said. "It is too early to know the fleet-wide impact of the recent finding."

For further evaluation and analysis, parts of the engine are sent to Pratt & Whitney's Engine Facility in Middletown, Connecticut.

"The F-35 is a huge problem because of its growing, already unaffordable, cost and its gigantically disappointing performance," the group's Winslow Wheeler said. "That performance would be unacceptable even if the aircraft met its far-too-modest requirements, but it is not."

The F-35 is Pentagon's most expensive weapons program in history with the total estimated cost of nearly $400 billion.

A watchdog group, the Project on Government Oversight, said the grounding was not likely to mean a significant delay in the effort to field the aircraft.

"The F-35 Joint Program Office is working closely with [engine maker] Pratt & Whitney and [primary plane manufacturer] Lockheed Martin at all F-35 locations to ensure the integrity of the engine, and to return the fleet safely to flight as soon as possible."

Friday's suspension is to of flight operations will remain in effect until an investigation of the problem's root cause is determined.