Argentina's president says an international search will continue for a submarine that has been lost in the South Atlantic for nine days.
The Argentine navy said an explosion occurred near the time and place where the submarine went missing on November 15 as it was sailing from the extreme southern port of Ushuaia to the coastal city of Mar del Plata.
The news of the explosion has lead some family members of the crew to give up hope of a rescue.
Navy officials and outside experts also worry that even if the sub is intact but submerged, its crew may be running out of oxygen.
President Macri said:
"It's a difficult moment for all, but obviously, especially for the families of the 44 crew members."
"I'm here to guarantee you that we will carry on with the search, especially now that we have the support of all the international community."
President Macri said the disappearance of the vessel will be looked into.
"This demands a serious, deep investigation," Mr Macri said.
"We need to understand how a submarine that had undergone a mid-life refit, and that was in perfect conditions to sail, suffered this explosion."
The UK is among those participating in the multinational search across an area of around 185,000 square miles, with RAF Voyager and C-130 aircraft and vessels HMS Protector and HMS Clyde giving assistance.
The Argentine navy said on Friday that Russia is sending an Antonov transport aircraft and a ship in the southern Patagonian port of Comodoro Rivadavia is being adapted to carry a US Navy submarine rescue chamber to the area.
The ARA San Juan, a German-built diesel-electric TR-1700 class submarine, was commissioned in 1985 and was most recently refitted in 2014.
The sub was originally scheduled to arrive on Monday at a navy base in Mar del Plata, about 250 miles south east of Buenos Aires.
Some relatives of the crew who have gathered at the base fear their loved ones will no longer be rescued.
"Hope is the last thing you lose. I'm waiting for a surprise, but I'm not really counting on it," Luis Tagliapietra, father of 27-year-old crew member Alejandro Damian Tagliapietra, said.
"You go from denial to suffering, from optimism to pessimism," he said, holding back tears.
When he found out about the explosion from his son's direct superior, he was told that there was a possibility there were no survivors.
"I asked them if they were all dead, and he said: 'Yes.'"
Cover image: Xinhua/TELAM/Argentinean Army/Juan Sebastian Lobos via Press Association.