Failed satellite calls that probably came from an Argentine navy submarine missing in the South Atlantic raised hopes Sunday that its 44 crew members are alive, but stormy conditions complicated the search.
Another official said earlier that the submarine reported a battery failure and was returning to base when it went missing Wednesday and lost contact with authorities.
A multinational air and sea search is under way with help from countries including Brazil, Britain, Chile, the United States and Uruguay.
Hopes of finding survivors were revived when the navy said Saturday that its bases had received seven satellite calls attributed to the submersible.
The calls came into different bases on Saturday between 10:52 a.m. and 3:42 p.m., according to CNN.
However, the navy was unable to confirm that those calls originated from the submarine.
The U.S. Navy said the Bluefin 12D diver can rescue six people at a time, if the Argentine submarine is found.
USA satellite company Iridium had earlier said that the submarine carried one of its satellite phones on board.
REUTERS The Argentine military submarine ARA San Juan and crew leaving the port of Buenos Aires in 2014
There is a feeling of "cautious enthusiasm", naval expert Fernando Morales told C5N television.
The submarine was 432km off Argentina's southern Atlantic coast when it sent its last communication early on Wednesday.
Rescuers are focusing on an ocean patch about 300 kilometers in diameter, radiating from the last point of contact.
HMS Protector has arrived in the search area around which worldwide efforts to find and rescue an Argentine submarine reported missing in the South Atlantic Ocean are centred. A Navy inquiry said the cause could not be definitively determined.
The Southern Command of the United States (SOUTHCOM), based in Miami Florida, reported that a US Military aircraft with a crew of 21 members will depart from Jacksonville, the northern part of the state of Florida, and is expected to arrive this Sunday in the South American country.
Argentina's president, Mauricio Macri, has travelled to the coastal city of Chapadmalal, near Mar del Plata, because of the situation. "Thank God", he said. It has been rehabilitated from 2007 to 2014, to extend to 30 years the duration of its life, and was "fully operational", having carried out several missions in 2017.
"We do not exclude any hypothesis", repeated the navy in its press releases. For the comfort of the crew and for the sake of speed, the San Juan would normally travel submerged at "snorkeling" depth, allowing the sub to run its diesel engines to power its electric drive and communicate through an antenna mast.
"The submarine surfaced and reported a malfunction, which is why its ground command ordered it to return to its naval base at Mar del Plata", he said.