Washington - The US military has concluded the remaining crew members of a B-52 bomber that crashed earlier this week off the coast of Guam are dead, the Air Force said Wednesday.

The B-52 crashed about 40 kilometres off Guam's northwest coast on Monday while it was preparing to participate in a ceremony recognizing the island's liberation. The cause of the crash has not been determined.

The bodies of two of the six crew were found on Monday and the other four remained missing.

"Officials here have determined that none of the six crew members survived the B-52 crash Monday off Guams northwest coast," The Air Force said. "Search and rescue teams have now shifted their focus from rescue operations to recovery of the aircrew."

The B-52, based out of Barksdale Air Force Base, Louisiana, was not carrying weapons. B-52s have been in service since 1955.

The accident is the second for the US Air Force this year on Guam. In February, a B-2 crashed at Andersen Air Force Base in the first- ever loss of a stealth bomber. The military estimated the loss of the aircraft at 1.4 billion dollars.