In a brief written statement, the Pentagon said it is too early to know the full impact of the newly discovered problem.
A watchdog group, the Project on Government Oversight, said the grounding is not likely to mean a significant delay in the effort to field the stealthy aircraft.
"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 the Pentagon's most expensive weapons program at a total estimated cost of nearly $400 billion. The Pentagon envisions buying more than 2,400 F-35s, but some members of Congress are balking at the price tag.
Friday's suspension of flight operations will remain in effect until an investigation of the problem's root cause is determined.
The Pentagon said the engine in which the problem was discovered is being shipped to a Pratt & Whitney facility in Connecticut for more thorough evaluation.
HAFB won't get work as result of F-35 troubles
Hill Air Force Base in Davis County is likely to get the job of maintaining F-35s, but is not yet a depot for such work.
Concerning the discovery of the fighter jet's cracked engine, base spokesman Rich Essary said Friday, "We're not going to do any work on this issue."