The U.S. military said it had grounded the entire fleet of 97 Lockheed Martin Corp. F-35 fighter jets until completion of additional inspections of the warplane's single engine, built by Pratt & Whitney, a unit of United Technologies Corp.

The Pentagon's F-35 program office, the Air Force and the Navy issued directives on Thursday ordering the suspension of all F-35 flights after a June 23 fire on an Air Force F-35A jet at Eglin Air Force Base in Florida, according to statements by the Pentagon and the F-35 program office.

The Pentagon said U.S. and industry officials had not pinpointed the cause of the fire, which occurred as a pilot was preparing for takeoff. The pilot was not injured.

The Pentagon said preparations were continuing for F-35 jets to participate in two U.K. air shows later this month, but a final decision would be made early next week. The fire has already derailed plans for an F-35 jet to fly by a naming ceremony for Britain's new aircraft carrier on Friday.