Argentina's navy could not confirm on Sunday, 19 November, if seven brief satellite calls received a day earlier had come from a missing submarine with 44 crew members on board.
"We do not have clear evidence that (the calls) have come from that unit," said Admiral Gabriel Gonzalez, commander of the Mar del Plata Naval Base. "We are analysing more closely to reliably determine that they were not calls coming from the submarine."
Gonzalez said the navy had intensified an aerial search off the country's southern Atlantic coast after adverse weather conditions triggered waves up to 26 feet (8 metres) and made a maritime search difficult.
Navy spokesman Enrique Balbi said the low-frequency satellite signals received on Saturday lasted a "few seconds", but had not connected with a base, partly due to inclement weather. The communication attempts were originally thought to indicate that the crew was trying to re-establish contact.
On Sunday, search units were largely relying on information gathered from a British polar exploration vessel, the HMS Protector, which was equipped with an underwater search probe and was following the path taken by the submarine, the ARA San Juan.
"Our thoughts remain with the crew of the ARA San Juan and their families at this time," said HMS Protector Commander Angus Essenhigh, according to a statement from Britain's Royal Navy.
The gesture has attracted attention since both nations fought a bloody war in 1982 after Argentine troops invaded the Falklands Islands.
Gonzalez also confirmed that the US Navy's Undersea Rescue Command had been deployed to the search area, along with aircraft from Argentina, Brazil and the US, alongside 11 surface vessels.
Among the 44 crew members is Eliana Krawczyk, the first female submarine officer in Argentina.
But Australian naval analyst James Goldrick, told news.com.au that it was highly unlikely they had survived after so long.
"Every hour, the likelihood of their being found alive diminishes," said the former rear admiral. "I don't hold up much hope of their being found. "It would be fantastic if it turns out it was just communications, but after this amount of time, I don't believe it will. "You'd be fearing the worst by now."
Authorities last had contact with the German-built, diesel-electric submarine on Wednesday as it sailed from the extreme southern port of Ushuaia to Mar del Plata.