The U.S. Navy announced Friday it will deploy its P-8A Poseidon maritime aircraft to assist in the search for the ARA San Juan, a missing Argentine submarine with 44 crew members on board.
The defence ministry has said the ARA San Juan appeared to try to make contact through seven failed satellite calls on Saturday between late morning and early afternoon.
However Admiral Gabriel Gonzalez, chief of the Mar del Plata Naval Base, said: "We do not have clear evidence that [the calls] have come from that unit", the Associated Press reported.
And now the US Navy is sending support to locate and rescue the ship from the sea. Those assets consist of a manned Submarine Rescue Chamber, or SRC, and a robotic underwater intervention system known as PRM.
President Mauricio Macri said the country will use "all resources national and international that are necessary to find the submarine".
It was unclear Sunday whether authorities could use the signal attempts to determine the sub's location.
Earlier Saturday, Navy spokesman Enrique Balbi said the area being searched off the country's southern Atlantic coast has been doubled as concerns about the fate of the submarine and its crew grew.
Despite the bad weather, "10 aircraft, both domestic and foreign, are in a search rotation 24 hours a day, each in a different area", he said.
Also, the British navy vessel Protector began a voyage Sunday to retrace the path that the San Juan was to have followed from Ushuaia, where it departed Monday, to the Mar de Plata naval base, its expected destination Sunday.
The Argentine military submarine ARA San Juan and crew are seen leaving the port of Buenos Aires in a file photo. The command includes a remotely operated vehicle and vessels capable of rescuing people from bottomed submarines. Among them was Ester Alfaro, mother of crew member Cristian Ibanez.
The families of the crewmembers are anxiously awaiting news of the missing submarine.
Special correspondents D'Alessandro reported from Buenos Aires and Kraul from Bogota, Colombia, respectively. Protocol calls for submarines to surface if communication is lost.
The Argentine navy says the missing diesel-electric submarine has enough oxygen, food and water to last at least two weeks.
Officials were investigating the possibility of a communication failure, according to Reuters.
The 213-foot long submarine was built in 1983 by Germany's Thyssen Nordseewerke.
The most likely scenario given is that an electrical problem may have unexpectedly cut off the vessel's communications.
It underwent a refit between 2007 and 2014 to extend its use by about 30 years.