A search is underway for a submarine and 44 crew who have been missing for two days.
Argentine naval officials said they had lost contact with the vessel off its southern coast - but insisted it was not yet considered lost.
Communication was last established with the German-built diesel-electric submarine on Wednesday and nothing has been heard from the crew since.
The Argentine Navy said ships and aircraft are searching near the last known location of the sub off the province of Chubut.
It also said officials are scanning all possible radio transmission frequencies for a sign of the San Juan.
Navy spokesman Enrique Balbi told the Todo Noticias channel there was no indication of problems from the submarine and said it could not yet be termed as lost.
"It's not that it's lost, because to be lost, you have to look for it and not find it," he said.
Admiral Gabriel Gonzalez, chief of the Mar del Plata base that was the submarine's destination, said the submarine had sufficient food and oxygen.
"We have a loss of communications, we are not talking of an emergency," he said.
Relatives of some of the crew members are at the base awaiting word of the search.
"We are praying to God and asking that all Argentines help us to pray that they keep navigating and that they can be found," said Claudio Rodriguez, brother of one of the crew members.
"We have faith that it's only a loss of communications."
Mr Balbi said the sub was headed from the naval base at Ushuaia in the country's extreme south to Mar del Plata, about 250 miles south of Buenos Aires.
The UK has offered to assist with a military aircraft on standby.
Additional reporting by PA