Argentina's navy has said that a mystery sound detected underwater did not come from a missing submarine with 44 crew members on board.
The noise - heard by two navy ships - had come from about 225 miles (360km) off the coast, and their position was in line with the path that ARA San Juan would have taken to reach its destination.
There was hope that the crew was making the "constant" sound to draw the attention of potential rescuers.
Navy spokesman Enrique Balbi has now confirmed the noise is unrelated to the vessel - and told reporters it had likely come from a "biological" source.
He added: "We all had hope, but unfortunately this comes from believing sources that are not trustworthy. Some sources were saying that this was banging on the hull in Morse code signals."
ARA San Juan disappeared around 430 km off Argentina's southern Atlantic coast on Wednesday, with the UK, US, Brazil, Chile and Uruguay all assisting in the search.
This is the latest setback for their operation. On Saturday, there was hope that the crew may have attempted to make contact through seven failed satellite calls - but it later emerged that these too were unrelated.
Initially the country's navy suspected that the submarine, which left the southern city of Ushuaia for Mar del Plata almost 3,000 km away, had suffered a communications problem.
The navy later revealed that it had reported a mechanical breakdown in its final transmission.
The crew were thought to have several days of food supply, but - unlike nuclear-powered UK and US submarines - the 66m long ARA San Juan is diesel electric, meaning that it has a finite supply of fuel, food and oxygen.
According to national Argentinian newspaper La Nacion, it was subjected to years of complex repair and engineering work in 2008, which the country's navy believed would extend its life by 30 years.
President Mauricio Macri tweeted that the Argentine government would "continue to deploy all available national and international resources" to find the submarine.