The US Coast Guard has found no sign of the submarine, which has been missing since Sunday in the North Atlantic.
The submarine was intended to monitor the wreckage of the Titanic and had five men on board when the ship had less than 40 hours of oxygen.
US Coast Guard Capt. Jamie Frederick acknowledged that the Canadian-backed search for the Titanic was “inconclusive,” he revealed during a press conference in Boston.
Officials said efforts to locate the submarine and the American, British and French nationals aboard it would continue.
Several companies organize multi-day trips to see the wreck of the Titanic, which lies 3,800 meters deep and about 640 kilometers off the Canadian island of Newfoundland.
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