Emergency signals believed to have come from Argentina's missing naval submarine ARA San Juan have been detected.
The Argentine Defence Ministry said seven failed "satellite calls" were picked up in a hopeful sign the crew of 44 was trying to re-establish contact.
The calls lasted between four and 36 seconds in the late morning and early afternoon on Saturday, the ministry said.
The ministry said it was working on tracing the location with an unnamed US company specialised in satellite communications.
Submarines which are stricken underwater can float a location beacon, known as an EPIRB, to the surface that can then emit emergency signals via satellite.
Whipping winds and more than 20ft waves in the South Atlantic have hindered international search efforts for the vessel.
The last confirmed location of the German-built ARA San Juan was 268 miles off Argentina's southern Atlantic coast on Wednesday.
It is thought the vessel, which has food and oxygen supplies for several days, may be suffering from a communications error.
Britain's Royal Navy has deployed HMS Protector, an ice patrol ship, to help in the search.
Argentina's President Mauricio Macri said the government was in contact with the crew's families.
"We share their concern and that of all Argentines," he wrote on Twitter.
"We are committed to using all national and international resources necessary to find the ARA San Juan submarine as soon as possible."
Pope Francis, who is from Argentina, has also offered his "fervent prayers" for the 44 crew members via a telegram to a senior bishop in the country.
The Pope expressed his spiritual closeness to the families of the sailors, as well as the military and civil authorities in Argentina.
Relatives and loved ones of the sailors have gathered at a naval base in Mar del Plata, where the submarine had been destined to arrive before vanishing, awaiting news.
"We're hopeful this will end soon to remain only as a bad memory," Maria Morales, the mother of one crew member told journalists.