All 44 crew members on a missing Argentinian submarine are feared dead after the navy announced a sound thought to be an explosion had been detected.
Relatives of the crew burst into tears, and some said they had lost all hope of rescue, after the briefing from the navy.
Spokesman Enrique Balbi said the search will continue until there is full certainty about the fate of the ARA San Juan.
He said evidence showed "an anomalous event that was singular, short, violent and non-nuclear that was consistent with an explosion".
"According to this report, there was an explosion," Mr Balbi told reporters. "We don't know what caused an explosion of these characteristics at this site on this date."
US and specialist agencies said the "hydro-acoustic anomaly" was produced just hours after the navy lost contact with the submarine on November 15.
The sub was originally scheduled to arrive on Monday at the Mar del Plata Navy Base, about 250 miles south-east of Buenos Aires. Relatives of the crew who have gathered at the base to receive psychological counselling broke into tears and hugged each other after they received the news.
Some clung to a fence crowded with blue-and-white Argentine flags, rosary beads and messages of support. Some declined to speak, while others lashed out in anger at the navy's response.
"They sent a piece of crap to sail," said Itati Leguizamon, wife of submarine crew member German Suarez. "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 German-built diesel-electric TR-1700 class submarine was commissioned in 1985 and was most recently refit in 2014.
During the 12 million US dollar retrofitting, the vessel was cut in half and had its engines and batteries replaced. Experts say that refits can be difficult because they involve integrating systems produced by different manufacturers and even the smallest mistake during the cutting phase of the operation can put the safety of the ship and the crew at risk.
The Argentine navy and outside experts have said that even if the ARA San Juan is intact, its crew might have only enough oxygen to be submerged seven to 10 days.
Authorities said late on Wednesday that Argentine navy ships as well a US P-8 Poseidon aircraft and a Brazilian air force plane would return to the area to check out the abnormal sound, which originated about 30 miles north of the submarine's last registered position.
The search location straddles the edge of the continental shelf, with widely varying ocean depths, some as great as 10,000 feet. Experts say the submarine could not have supported pressures that far down.
"If a submarine goes below its crush-depth, it would implode, it would just collapse," said James H Patton Jr a retired Navy captain.
"It would sound like a very, very big explosion to any listening device."
Whatever it was, US Navy Lieutenant Lily Hinz said the sound detected "was not a whale, and it is not a regularly occurring sound".
The San Juan lost contact as it was sailing from the extreme southern port of Ushuaia. The submarine's captain had reported a battery failure.
More than a dozen planes and ships have been participating in the multinational search despite stormy weather that has caused waves of more than 20 feet. Search teams are combing an area of some 185,000 square miles, which is roughly the size of Spain.
The US government has sent two P-8 Poseidons, a naval research ship, a submarine rescue chamber and sonar-equipped underwater vehicles. US Navy sailors from the San Diego-based Undersea Rescue Command are also helping with the search.
The UK's Ministry of Defence sent a special airplane with emergency life support pods to join the hunt that includes planes and ships from a dozen nations.
Hopes were buoyed after brief satellite calls were received and when sounds were detected deep in the South Atlantic. But experts later determined that neither was from the missing sub.
"They haven't come back and they will never come back," said Jesica Gopar, wife of submarine officer Fernando Santilli, choking back tears. "I had a bad feeling about this and now it has been confirmed."