The Argentinian navy on Monday detected noises that officials believe could be from Argentina's missing submarine, the ARA San Juan.
The San Juan, which has a crew of 44, was last heard heard from on Wednesday before it went missing in the Atlantic Ocean.
A senior U.S. Navy official familiar with the service's assistance in the search for the submarine told CNN that the sonar systems of two ships picked up noises that sounded like tools being banged against the hull of a submarine. The official noted that crews of submarines in distress bang on the vessel's hull to alert passing ships to their location.
The Argentinian navy is focusing its search in an area of 35 square nautical miles about 330 miles from the coast of Argentina.
Satellite calls thought to be from the San Juan did not help rescuers, who have been unable to locate the submarine's position.
The U.S. and other countries are assisting Argentina in its search for the San Juan. The German-built diesel-electric submarine can be aided by a deep submergence rescue vehicle if it cannot surface.
Recent bad weather in the region has made the search more difficult for aircraft and ships; the Patagonia Coast is known for bad storms.