Argentina’s Navy said on Wednesday that an unusual noise in the South Atlantic Ocean was found to have come hours after it lost touch with a submarine that has been missing for over a week. The new information means the search operation will now move back to an area which has already been searched, AP reported.

Over a dozen countries are involved in the search operation, even as the oxygen supply in the ARA San Juan is expected to have nearly run out. Forty-four crew members are on board.

The Navy refused to confirm whether the noise was an explosion.

The “hydro-acoustic anomaly” was detected in the ocean three hours after the last communication on November 15, about 48 km north of its last known position, a Navy spokesperson said, adding, “We are in a very dangerous situation, and one that is getting worse.”

The submarine has only enough air to last seven to 10 days if it has remained fully immersed since it disappeared, CNN reported. However, if it came up to the water surface or “snorkeled” – raised a tube to the surface to get air – then crew could survive longer.

Reports earlier said the submarine had reported a mechanical breakdown in its last communication.

Over a dozen boats and aircraft from Argentina, the United States, Britain, Chile and Brazil are looking for the missing submarine, though the search operations have been hampered by storms in the region. Russia has also joined the search, BBC reported.