Argentina's navy has said it is analysing a noise that might have come from a missing submarine with 44 crew members on board.
Navy spokesman Enrique Balbi said a US aircraft was sent to check an area where the noise was heard by two Argentine Navy ships.
The noise was heard in the South Atlantic about 220 miles (360km) from the Argentine coast and at a depth of about 650ft (200m).
Another official said earlier that the submarine reported a battery failure and was returning to base when it went missing last Wednesday and lost contact with authorities.
The sub was journeying from the extreme southern port of Ushuaia to the coastal city of Mar del Plata.