Hopes that the 44 crew of a missing Argentine submarine might still be alive have been dashed after the navy said an event consistent with an explosion had been detected.
The "abnormal, singular, short, violent, non-nuclear event" was recorded in the south Atlantic by a nuclear test watchdog last week.
Relatives of the missing crew reacted with grief and anger at the news.
It follows a US report of a loud noise in the same area.
The ARA San Juan disappeared last Wednesday. More than a dozen countries including the US, Russia and the UK have sent assistance.
It was provided to the Argentine navy on Thursday by the Vienna-based Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO), spokesman Capt Enrique Balbi said.
In a statement, the CTBTO said two of its hydro-acoustic stations had detected a signal from an "underwater impulsive event".
On Wednesday the navy received a US report of a "hydro-acoustic anomaly" detected hours after the submarine went missing.
Capt Balbi said the suspected explosion took place near the submarine's last known location.
The navy only knew the location of the suspected explosion, not its cause, he said, and search efforts would be concentrated in the area.