(CNN) -- The Pentagon has grounded its fleet of F-35 fighter jets after a runway fire at Eglin Air Force Base in Florida.
"The root cause of the incident remains under investigation," Pentagon spokesman Rear Adm. John Kirby said. "Additional inspections of F-35 engines have been ordered, and return to flight will be determined based on inspection results and analysis of engineering data."
The fire happened June 23. Additional details were not immediately available.
Last year, the U.S. military grounded the F-35 because of a crack in an engine component that was discovered during a routine inspection in California.
The nearly $400 billion Joint Strike Fighter is the Pentagon's most expensive weapons system program. It has been beset by cost overruns and various technical problems during development.
The U.S. military describes the jet as the "next generation strike aircraft weapon for the Navy, Air Force, Marines and our allies." It also says the fighter will be "the most affordable, lethal, supportable and survivable aircraft ever to be used by so many warfighters across the globe."