After days of searching for its missing submarine with 44 crew aboard, Argentina's navy received distress signals late Saturday, authorities said.
There had been no contact with the ARA San Juan since early Wednesday, according to the navy, prompting Buenos Aires to launch an air and sea search with help from countries including Brazil, Britain, Chile and the United States.
The entire search area has been scoured by ships and aircraft, despite storm conditions that complicated the effort, Argentine navy spokesman Enrique Balbi said.
Seven satellite-transmitted signals believed to be part of the vessel trying to resume contact were detected, the Defense Ministry said.
The signals were unable to lock in and connect with communications bases, the military explained.
With the help of US satellite communication experts, the signals were detected at 10:52 am (1352 GMT) and 3:42 pm (1842 GMT) on various naval bases, but did not lock in, thus preventing a full connection.
"Right now, we are working to pinpoint the exact location of what is emitting the signals," presuming that it could be the missing sub, the ministry said.
Brazil, Britain, Chile, the United States and Uruguay took part in the aerial side of the search, and the United States said it was sending rescue help.
The California-based Undersea Rescue Command was deploying two independent rescue assets -- including a pressurized rescue module -- to help in the hunt for the missing sub.
Argentine President Mauricio Macri said on his Twitter account that "we will do what is necessary to find the submarine as soon as possible."
TR-1700 class diesel electric submarine had been returning from a routine mission to Ushuaia near the southernmost tip of South America, to its base at Mar del Plata, around 400 kilometers (250 miles) south of Buenos Aires.
Among those on board is Argentina's first female submarine officer, 35-year-old weapons officer Eliana Krawczyk.
The San Juan is one of three submarines in the Argentine fleet.
Sixty-five meters (213 feet) long and seven meters (23 feet) wide, it was built by Germany's Thyssen Nordseewerke and launched in 1983.
It underwent a re-fit between 2007 and 2014 to extend its usefulness by some 30 years.
