Rescuers searching for a missing Argentinian naval submarine are trying to pinpoint the location of emergency signals, although they do not know whether they originated from the vessel.
Seven failed satellite calls were received on Saturday, Argentina's defence ministry said, raising hopes that the 44 crew members on board ARA San Juan were trying to re-establish contact.
However, Admiral Gabriel Gonzalez, chief of the Mar del Plata Naval Base, said the navy did "not have clear evidence" that the calls "have come from that unit".
"We are analysing more closely to reliably determine that they were not calls coming from the submarine," the admiral added.
The UK, US, Brazil, Chile and Uruguay have joined the search operation for the submarine, which disappeared 268 miles off Argentina's southern Atlantic coast on Wednesday.
Claudio Rodriguez, whose brother Hernan is on board the submarine, said the satellite signals suggested the vessel was still afloat and would be found.
"They've got to be afloat. Thank God," he said.
"That gives us hope, because we knew that if they were down below, they would be screwed."
A spokesman for Argentina's defence ministry said it was "working to pinpoint the exact location of what is emitting the signals".
It is thought the vessel, which has food and oxygen supplies for several days, may be suffering from a communications error.
The Royal Navy has deployed HMS Protector, an ice patrol ship, to help in the search.
Britain also has a C-130 Hercules, which is stationed in the Falklands Islands, on standby if required.
A second US Navy aircraft has joined the search, while two underwater crafts designed to rescue trapped submarine sailors at different depths are being deployed.
A remotely operated underwater robot known as an ROV is also being used.
Argentinian President Mauricio Macri wrote on Twitter: "We will do what is necessary to find the submarine as soon as possible."
Relatives of the missing sailors have gathered at a naval base in Mar del Plata, where the submarine had been destined to arrive before vanishing, awaiting news.
Maria Morales, the mother of one crew member told journalists, told reporters: "We're hopeful this will end soon to remain only as a bad memory."