5 Marines missing off coast of Japan declared dead originally appeared on abcnews.go.com

The five Marines missing off the coast of Japan for nearly a week following an aviation mishap have been declared dead by the U.S. Marine Corps.

The Marines were aboard a KC-130 refueling aircraft that may have been attempting to refuel in midair an F/A-18 fighter jet on Wednesday.

"The Marine Corps has pronounced the five remaining Marines involved in the F/A-18 and KC-130 aviation mishap deceased," according to a statement from the III Marine Expeditionary Force based in Japan. "The change in status comes at the conclusion of search and rescue operations."

"Every possible effort was made to recover our crew and I hope the families of these selfless Americans will find comfort in the incredible efforts made by US, Japanese, and Australian forces during the search," U.S. Marine Corps Lt. Gen. Eric Smith, commanding general, III Marine Expeditionary Force, said in the statement.

(MORE: Marines identify killed F/A-18 pilot as search continues for 5 missing off coast of Japan)

The accident happened about 200 miles off the southwest coast of Japan. The Marine Corps has not confirmed that an aerial refueling was in progress at the time of the mishap.

Four hours after the mishap, one of the two pilots aboard the fighter jet was rescued by the Japanese Maritime Self Defense Forces. Capt. Jahmar F. Resilard, 28, was recovered six hours later but pronounced deceased.

Both pilots had been able to eject from the F/A-18, but the refueling tanker isn't equipped with ejection seats.

Over the next six days U.S., Japanese and Australian military aircraft and ships covered more than 35,000 square miles of ocean searching for the five Marines.

(MORE: Military plane crash latest in string of deadly aviation incidents)

"It is with a heavy heart that we have shifted to recovery operations," said U.S. Air Force Lt. Gen. Jerry Martinez, commander of U.S. Forces Japan. "I ask that you please keep the families and friends of these Marines in your thoughts during this incredibly difficult time."

"I am incredibly proud of and grateful for the efforts of the U.S. military along with our Japanese and Australian partners," Martinez added. "Support from the Japan Self Defense Forces and Coast Guard was immediate and life-saving, and I thank them for their professionalism, dedication and robust support throughout this massive operation."

The names of the five Marines will be made public 24 hours after their families are notified.