Argentina's navy says noises detected near where a submarine went missing last week did not correspond with a typical distress signal and were not believed to have come from the vessel.
The sounds had raised hopes that those among the 44-member crew of the ARA San Juan were intentionally signaling search crews in the South Atlantic Ocean.
The navy also said Monday that the submarine reported electrical problems and had been ordered to return to port in Mar del Plata, 400 kilometers south of Buenos Aires, when it disappeared.
Brazil, Chile, Uruguay, Peru, the United States, and Britain have all joined the search effort that has been hampered by high winds and waves.
Britain, which fought a war with Argentina in the 1980s, is using an Arctic research vessel with scientific sensors in the search. The United States has sent a NASA research plane, a submarine-hunting plane, along with a submarine rescue team.
The 66 meter long, German-built diesel-electric submarine has been in service since 1985. Argentina's first female submarine officer (Eliana Krawczyk) is a member of the crew.