UPDATE 25 November 2:30pm (GMT): Argentina says the sound detected in missing submarine search is consistent with an explosion.
Navy spokesman Enrique Balbi said that the relatives of the crew have been informed and that the search will continue until there is full certainty about the fate of the ARA San Juan. He said there was no sign the explosion might be linked to any attack on the sub.
ORIGINAL STORY: Ships and planes hunting for a missing Argentine submarine with 44 crew members will return to a previously searched area after officials said Wednesday (22 November) that a noise made a week ago in the South Atlantic could provide a clue to the vessel's location.
Balbi said the "hydro-acoustic anomaly" was determined by the US and specialist agencies to have been produced on 15 November, just hours after the final contact with the ARA San Juan, and could have come from the sub.
The sound originated about 30 miles north of the submarine's last registered position, he said.
"It's a noise. We don't want to speculate [about what caused it]," Balbi said.
He said Argentine navy ships as well as a US P-8 Poseidon aircraft and a Brazilian air force plane would return to the area to check out the clue, even though the area already was searched.
US Navy Lt. Lily Hinz later said the unusual sound detected underwater could not be attributed to marine life or naturally occurring noise in the ocean. She declined to speculate whether it might have been an explosion, saying experts did not know what it was.
"It was not a whale, and it is not a regularly occurring sound," Hinz said.
On land, relatives of the submarine's crew grew increasingly distressed as experts said the vessel lost for seven days might be reaching a critical period of low oxygen.
Jorge Villarreal kept his eyes fixed on the ocean, hoping to catch a glimpse of the vessel that carried his son Fernando, a submarine officer.
"As a dad I want him to be rescued immediately, but we can't forget about the inclemency of the weather. And the foreign help just doesn't come from one day to the next," he said. "We hope this will go right because of the improving weather and the technology that's being used."
The San Juan went missing as it was sailing from the extreme southern port of Ushuaia to the city of Mar del Plata, about 250 miles (400 kilometers) south east of Buenos Aires.
The Argentine navy and outside experts worry that oxygen for the crew would last only seven to 10 days if the sub was intact but submerged. Authorities do not know if the sub rose to the surface to replenish its oxygen supply and charge batteries, which would affect the calculation.
The German-built diesel-electric TR-1700 class submarine was scheduled to arrive on Monday at the naval base in Mar del Plata, where city residents have been dropping by with messages of support for relatives of the crew.
More than a dozen airplanes and ships are participating in the multinational search despite stormy weather that has caused waves of more than 20 feet (6 meters). Search teams are combing an area of some 185,000 square miles (480,000 square kilometers), which is roughly the size of Spain.
The US government has sent two P-8 Poseidons, a naval research ship, a submarine rescue chamber and sonar-equipped underwater vehicles. US Navy sailors from the San Diego-based Undersea Rescue Command are also helping with the search.
President Donald Trump went on Twitter to offer his good wishes to Argentina on Wednesday, though he inflated the number of missing sailors by one.
"I have long given the order to help Argentina with the Search and Rescue mission of their missing submarine. 45 people aboard and not much time left. May God be with them and the people of Argentina!" his tweet said.
Britain's Ministry of Defense has deployed another aircraft. The RAF Voyager landed in Argentina on Wednesday, some 35 years after the UK waged a brief war with the country over possession of the Falkland Islands/Malvinas.
The helicopter is packed with equipment, including 12 emergency life support pods. It joins HMS Protector, a Royal Navy ice patrol ship; the HMS Clyde, an offshore patrol vessel; and an RAF C-130 in the search.
Hopes were lifted after brief satellite calls were received and when sounds were detected deep in the South Atlantic. But experts later determined that neither was from the missing sub. A US Navy aircraft later spotted flares and a life raft was found in the search area, but authorities said neither came from the missing submarine.
The false alarms have rattled nerves among distraught family members. Some have begun to complain that the Argentine navy responded too late.
"They took two days to accept help because they minimised the situation," Federico Ibanez, the brother of submarine crew member Cristian Ibanez, told The Associated Press.
The navy has said the submarine reported a battery failure before it went missing. Authorities have no specific details of the problem.
"I feel like authorities let too much time pass by and decisions were taken late," Ibanez's sister, Elena Alfaro, said outside the base. "And yet, I still carry some hope."