TOKYO — Five United States Marines were declared dead on Tuesday, six days after they went missing when two aircraft crashed off the coast of Japan during a routine training exercise.

The deaths follow a growing number of recent American military accidents, including two deadly collisions involving American warships in 2017, and will likely sharpen the spotlight on the country’s military operations in Asia.

After a search and rescue operation that has encompassed over 800 hours and covered 35,000 square miles of ocean, the bodies of the five missing Marines have yet to be recovered.

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