The US has concluded a search and rescue operation for seven marines and a sailor missing at sea for days after an amphibious assault vehicle (AAV) sank during an exercise.

Missing members are presumed dead after the leadership determined that there is little probability that they are alive given the circumstances of the incident.

The operation will now be shifted to recover the remains of the missing service members.

The marines involved in the accident belonged to Camp Pendleton-based 15th Marine Expeditionary Unit (MEU).

15th MEU Commanding Officer Colonel Christopher Bronzi said: “It is with a heavy heart that I decided to conclude the search and rescue effort.

“The steadfast dedication of the marines, sailors, and coast guardsmen to the persistent rescue effort was tremendous.”

The incident happened late last week when an AAV sank during a routine training exercise off the coast of San Clemente Island, California.

A total of 16 members, including 15 marines and one sailor, were on the vehicle. Eight were rescued, with one later dying.

During the 40-hour rescue mission, helicopter, ships and watercraft searched more than 1,000 square nautical miles.

The circumstances that led to the incident are currently being investigated.

Bronzi added: “Our thoughts and prayers have been, and will continue to be with our marines’ and sailor’s families during this difficult time.

“As we turn to recovery operations we will continue our exhaustive search for our missing marines and sailors.”