Water entered the snorkel of an Argentinian submarine and caused one of its batteries to short circuit before the vessel went missing 12 days ago, a navy spokesman has said.
Hopes for survivors have been largely crushed by reports of an explosion detected near the time and place where the ARA San Juan was last heard from on November 15.
Since then, there have been no signs of the sub or debris despite an intensive multinational search.
Experts have said the crew had only enough oxygen to last up to 10 days if the sub remained intact but submerged.
The navy said last week that before the submarine went missing, the captain reported an electrical problem in a battery compartment and the vessel was ordered to return to its base in the coastal city of Mar del Plata, about 250 miles southeast of Buenos Aires.
Navy spokesman Enrique Balbi told reporters on Monday that the captain said water had entered through the snorkel when the sub was charging batteries.
The water went 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", he said.
Mr Balbi said the captain later communicated by satellite phone that the problem had been contained.
"They had to electrically isolate the battery and continue sailing underwater to Mar del Plata using another battery circuit," Mr Balbi said.
The San Juan, a German-built diesel-electric TR-1700 class submarine, was commissioned in 1985 and was most recently refitted in 2014.
Some family members have denounced the navy's response to the disappearance and the age and condition of the vessel.
President Mauricio Macri has promised an investigation.
The navy says more than a dozen countries are still helping search for the sub in area where the explosion was recorded about 270 miles off the coast of Argentina.
Mr Balbi said a Norwegian ship carrying the US Navy's underwater remotely operated vehicle and its pressurised rescue module was expected to arrive to the search zone later on Monday.