Argentina's navy could not confirm Sunday if seven brief satellite calls received a day earlier 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 Adm. Gabriel Gonzalez, commander of the Mar del Plata Naval Base. "We are analyzing more closely to reliably determine that they were not calls coming from the submarine."
Gonzalez said the navy had intensified an aerial hunt off the country's southern Atlantic coast after adverse weather conditions spurred waves up to 26 feet (8 meters) and made a maritime search difficult.
Navy spokesman Enrique Balbi said the low-frequency satellite signals received 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 Cmdr. Angus Essenhigh, according to a statement from Britain's Royal Navy.
The gesture has attracted attention since the nations fought a bloody war in 1982 after Argentine troops invaded the Falklands Islands.
Gonzalez also confirmed that the U.S. Navy's Undersea Rescue Command had been deployed to the search area, along with aircraft from Argentina, Brazil and the U.S., and 11 surface vessels.
Among the 44 crew members is Eliana Krawczyk, the first female submarine officer in Argentina.
Authorities last had contact with the German-built, diesel-electric sub on Wednesday as it was sailing from the extreme southern port of Ushuaia to Mar del Plata.