Buenos Aires - The blurry sonar image of an object deep in the South Atlantic was a sunken fishing vessel not an Argentine submarine that went missing on November 15 with 44 crew members, the country's navy said on Saturday, ending hopes that the sub had been located.

Rescuers had sent an unmanned Russian submersible to review the 60-metre-long object located at 477 metres below sea level.

The missing submarine, the ARA San Juan, was roughly that length — 66 metres — and officials said the image was "unclear". They sent the submersible to "visually verify" if it was indeed the San Juan.

"It was confirmed that it wasn't the submarine's shell" but a sunken fishing vessel, Argentine navy spokesperson Enrique Balbi said later on Saturday.

The navy "regrets that without a rigorous analysis expectations were generated in the families and society, which must now face another frustration," Balbi said.

Before Balbi's announcement, authorities had said that if the image did not reveal any new clues, the search would focus on other signals of interest detected in parts of the South Atlantic where the vessel was last heard from.

Search, not rescue

Argentina's navy said on Thursday that it is no longer looking for survivors although a multinational operation will continue searching for the vessel.

"The extreme environment, the time elapsed and the lack of any evidence eliminates a scenario compatible with human life," Balbi said. "These are hours of intense pain and anguish (for relatives) in light of the loss of their loved ones, our 44 comrades."

The German-made submarine went missing as it was journeying from the extreme southern port of Ushuaia to the city of Mar del Plata, about 400km southeast of Buenos Aires.

The navy has said the vessel's captain reported that water entered the snorkel and caused one of the submarine's batteries to short circuit. An explosion was later detected around the time and place where the San Juan last made contact.