Shortly before the ARA San Juan submarine went missing off the coast of Argentina 12 days ago, water entered the snorkel and caused one of the vessel's batteries to short circuit, the navy has said.
Argentina's navy lost contact with the submarine on 15 November after the vessel's captain reported a "short circuit" in the battery system.
Navy spokesperson Enrique Balbi said on Monday (27 November) that the short circuit was triggered when water got into the snorkel where the submarine's batteries were being charged.
Balbi said that water moved through the ventilation system to a battery connection tray in the prow and "caused a short circuit and the beginning of a fire, or smoke without flame."
The navy has said that "an explosion" appears to have taken place on the submarine shortly after it lost contact.
Concern over the survival of the 44 crew members on board is mounting after it emerged that the submarine only had a 10-day oxygen supply if the submarine remained intact and submerged.
There have been no sightings and no debris has been found. On Monday, Balbi said that he had not ruled out an "extreme survival situation" and that the multinational search would continue.
The US' navy Undersea Rescue Command sent a ship to the search zone, 430km (267 miles) off Argentina's southern coast, on Sunday (26 November). The rescue mission includes around 30 ships and planes manned by 4,000 personnel from 13 countries.
Relatives have expressed anger over the state of the submarine which was built in 1985. The submarine was refurbished in 2014, when its engine and batteries were replaced.
Itati Leguizamon, wife of submarine crew member German Suarez, told the Associated Press: "They sent a piece of crap to sail. They inaugurated a submarine with a coat of paint and a flag in 2014, but without any equipment inside. The navy is to blame for its 15 years of abandonment."
The submarine had been expected to dock at the port of Mar del Plata on 19 November.