The US Coast Guard says it is opening an investigation into the cause of the implosion of a submersible headed to the wreck of the Titanic. It also announced the end of its search for the five people on board.

The Coast Guard revealed on Sunday that it convened a Marine Board of Investigation, or MBI, into the loss of the Titan submersible. An MBI is the highest level of investigation in the Coast Guard.

It said its investigators are in an initial evidence collection phase, including debris salvage operations. It added they are taking all precautions on site if human remains are encountered.

The submersible went missing after diving into the North Atlantic on June 18. Rescue crews from the United States and Canada discovered debris from the sub on the ocean floor four days later.

The Coast Guard said on Thursday that the debris is consistent with the catastrophic loss of the pressure chamber, suggesting that all five on board died.

It says its investigators are working in close coordination with authorities from Canada, France and Britain. It says it aims to prevent a similar occurrence by making necessary recommendations.