A total of 15 countries, including the United States, Britain, Russia and France, are helping to search for the ARA San Juan, which has 44 crew members on board. It last made contact with Argentina's navy on November 15.
The search operation extends for a 22-mile (35-kilometer) radius from an area about 250 miles off the coast of Argentina -- around the location of the explosion that may have sent the vessel to the bottom of the ocean.
"Unfortunately, we still have not located or detected the San Juan submarine," Navy spokesman Enrique Balbi said Monday in Buenos Aires.
Balbi also confirmed the Russian navy's intelligence ship Yantar -- equipped with a submarine capable of descending 6,000 meters underwater -- will arrive to assist with the search on December 5.
The ARA San Juan's camouflage-focused design has frustrated efforts, along with other factors including poor weather, according to US Navy pilot Adam Slavinsky, who said search crews "have no deadline" to find the vessel.
From Argentina's military base at Bahia Blanca, two US Navy P-8A Poseidon aircraft have been using their radar and scanners in the sub hunt, dropping buoys equipped with sensors to try to detect the vessel.
A ship equipped with an underwater emergency vehicle -- which can be deployed to the bottom of the ocean -- is also being used in the search effort.
Three San Juan crew members miraculously escaped the tragedy -- one had rushed to their ill mother's bedside, another was reassigned to a mission in Peru, and the third was sent to perform administrative duties.
The loss of the submarine represents a huge blow to the already under-equipped Argentine military.
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