Argentina's Navy cannot confirm whether seven brief satellite calls received the day before were from a lost 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, chief of the Mar del Plata Naval Base.
"We are analysing more closely to reliably determine that they were not calls coming from the submarine."
Admiral Gonzalez said the Navy has intensified its aerial search off the country's southern Atlantic coast after adverse weather conditions spurred 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 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 the Royal Navy.
The gesture has attracted attention since the nations fought a bloody war in 1982 after Argentina invaded the Falklands Islands.
Gonzalez also confirmed the US Navy's Undersea Rescue Command had been deployed to the search area, along with aircraft from Argentina, Brazil and the US, and 11 surface vessels.
Among the 44 crew members is Eliana Krawczyk, the first female submarine officer in Argentina.
Authorities said the submarine left the extreme southern port of Ushuaia on Wednesday and lost contact as it was heading to Mar del Plata, a city on the country's north-east coast.