The US military has suspended all test flights for its F-35 fighter jet over potential engine problems, officials said.
Friday’s decision was described as a "precautionary measure" after a crack was discovered on a turbine blade in one F-35 engine at Edwards Air Force Base in California.
"It is too early to know the fleet-wide impact of this finding, however as a precautionary measure, all F-35 flight operations have been suspended until the investigation is complete and the cause of the blade crack is fully understood," programme spokeswoman Kyra Hawn said in a statement.
The suspension applies to all 51 jets in the F-35 fleet.
"We have to find out if this is an isolated incident or if it has design implications," Hawn said.
The cracked turbine blade was being shipped to manufacturer Pratt and Whitney's engine plant in Middletown, Connecticut for evaluation.
The Pentagon has high hopes for the radar-evading F-35 fighter, which is supposed to replace most of the combat aircraft fleet of the US air force, navy and Marine Corps by the end of the decade.
The defence department plans to produce 2,443 aircraft for the US military and several hundred others for eight international partners who have invested in the project, as well as at least two customers, Japan and Israel.
But countries taking part in the programme are anxious about spiraling costs and incessant production delays, with some postponing or cutting investments.