Argentina says it is accelerating the search for a submarine that has been lost in the South Atlantic for nine days.
The announcement comes amid growing fears for its 44 crew members.
The Argentine navy says an explosion occurred near the time and place where the sub went missing on November 15.
But spokesman Enrique Balbi said the international search continues.
He said Russia is sending an Antonov transport aircraft. And a ship is being adapted in the southern Patagonian port of Comodoro Rivadavia to carry a US Navy submarine rescue chamber to the area.
Argentine navy officials worry that even if the ARA San Juan is intact but submerged, its crew may be running out of oxygen.
Families of the 44 crew on a missing submarine in the South Atlantic say they've given up hope.
The statement comes after the Argentinian navy said there was a suspected explosion hours after the 'San Juan' was last seen nine days ago.
However the MoD have told Forces News that British assets will keep searching for the submarine until the Argentines tell them not to.
Defence Secretary Gavin Williamson has offered Britain's "sincerest condolences" to Argentina amid fears that all 44 crew members on a missing submarine have died.
Following the announcement, Mr Williamson said this is "truly devastating" for everyone involved:
"When it comes to situations like this, nationality doesn't matter: all sailors have an obligation to help each other in a time of such desperate need.
"I'm extremely proud of the role our Navy and Air Force have played in the international effort to help, and I speak on behalf of those involved, and the whole country, in offering our sincerest condolences to Argentina and the family and friends of the crew."
Argentinian navy spokesman Enrique Balbi has said the search will continue until there is full certainty about what happened to the San Juan.
Yesterday Argentina said a sound detected in the search for a missing submarine with 44 crew members on board is consistent with a non-nuclear explosion.
Navy spokesman Enrique Balbi said the relatives of the crew have been informed.
The search will continue until there is full certainty about the fate of the ARA San Juan.
Ships and planes have returned to a search area to check on the noise that experts say could provide a clue to the vessel's location.
US and specialist agencies say the "hydro-acoustic anomaly" was produced just hours after the navy lost contact with the submarine on November 15.
Experts worry that if the ARA San Juan is intact but submerged, its crew might have only enough oxygen to last seven to 10 days
However, Argentina have said that there is no evidence of an attack on the missing submarine.
This morning, an RAF aircraft landed in Argentina some 35 years after the Falklands War, as it joins search efforts to find a missing submarine with 44 sailors on board.
The Argentine navy said it lost contact with the ARA San Juan on 15th November as the submarine sailed from the extreme southern port of Ushuaia to Mar del Plata.
Since then, more than a dozen international vessels and aircraft, including those from the UK, have joined the search - with efforts hindered by stormy weather and 20ft waves.
A spokesman for the Ministry of Defence (MoD) said an RAF Voyager, which took off from Brize Norton, Oxfordshire, arrived in Argentina on Wednesday.
It is understood the landing of the Voyager marks the first time in as many years that an RAF aircraft which departed from the UK has landed in the South American country.
The MoD spokesman said the Voyager is packed with three tonnes of equipment, including 12 deep emergency life support pods.
HMS Protector, a Royal Navy ice patrol ship, was deployed to the vessel's last known location, and used its sonar equipment to search below the waves for the missing sub.
An RAF C-130 has also joined the search following an offer of assistance, and members of the specialist Submarine Parachute Assistance Group are also offering expert advice.
HMS Clyde, an offshore patrol vessel, which was returning from a patrol to South Georgia has also assisted with the search efforts.
With enough food, oxygen and fuel for the crew to survive 90 days on the sea's surface, the sub only has enough oxygen to last seven days when submerged, the Argentine navy said.
A well-established convention enshrined in international law means all sailors have an obligation to assist others in distress, irrespective of nationality.
The international search teams are combing the waters in a wide area of some 185,000 square miles (480,000 square kilometres), which is roughly the size of Spain.
Now missing for a week, Argentina is leading the search for their sailors, and the United States is coordinating the international response.
So far sounds detected under the sea, thought at the time to have come from the missing submarine, and seven brief satellite calls believed to have since been made by the crew, have been ruled out as coming from the lost vessel.
Cover picture courtesy of the British Embassy in Argentina.