PENSACOLA, Fla. - Two fighter jets went missing during a training exercise over the Gulf of Mexico on Wednesday, but the pilots were later rescued, the U.S. air force said.

Eglin Air Force Base spokeswoman Shirley Pigott said the pilots were rescued after their single-seat F-15C Eagles disappeared Wednesday afternoon off the Florida Panhandle, about 55 kilometres south of Tyndall Air Force Base.

The air force has not determined if the planes collided or why they might have crashed. Weather in the area was clear.

More than 60 Coast Guard personnel had been involved in the search using multiple helicopters, cutters and jets, said Coast Guard Petty Officer James Harless. Air force officials are investigating.

The air force grounded all of its F-15s -- nearly 700 -- after the catastrophic failure of an F-15C during a routine training flight in Missouri in November. The pilot safely ejected.

Most were back in service by January, but others were grounded indefinitely after defects were found.

The air force began using the F-15C in 1979. The planes, built by McDonnell Douglas Corp., were deployed to the Persian Gulf in 1991 in support of Operation Desert Storm and have since been used in Iraq, Turkey and Bosnia.

The planes can fly up to 20,000 metres and each costs about $30 million, according to the air force.