San Francisco, Aug 3 : Eight US troops, who went missing in a training accident last week, have been presumed dead as search and rescue operation off the California coast has ended, the military said. "After an extensive 40-hour search, the 15th Marine Expeditionary Unit (MEU), I Marine Expeditionary Force (MEF), and the Makin Island Amphibious Ready Group (ARG) concluded their search and rescue operation for seven missing Marines and one Sailor," Xinhua news agency reportedciting the I Marine Expeditionary Force as saying in a statement on Sunday. The accident took place on July 30 when an amphibious assault vehicle carrying 15 Marines and one Navy sailor began to take on water during a training exercise near San Clemente Island. One Marine was killed and two were injured in the accident while other Marines were rescued, the Marine Corps said previously. "It is with a heavy heart, that I decided to conclude the search and rescue effort," said Col. Christopher Bronzi, 15th MEU Commanding Officer, in the statement. "I know all of us in the USMC family are extremely saddened following the announcement of the end of SAR (search and rescue) operations," US Marine Corps Commandant Gen. David Berger tweeted Sunday morning. "This difficult decision was made after all resources were exhausted. Our prayers continue to be with the family and friends of the eight Marines and one sailor we lost," he noted. Officials said that efforts will now turn to finding and recovering the missing service members. Over the course of the at-sea search, rescue helicopters, ships and watercraft searched more than 1,000 square nautical miles. The circumstances surrounding the mishap are being investigated, according to the press release. /IANS