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Argentina‘s navy revealed Monday that a submarine missing for five days reported a mechanical breakdown in its final communication, and that weekend signals did not come from the vessel, dimming hopes for its 44 crew members.

The nature of the breakdown was not immediately clear. It was the first time the navy indicated it had been aware of a problem.

“The vessel surfaced and it reported a breakdown. It was therefore asked to change course and go to Mar del Plata,” said Gabriel Galeazzi, the head of the naval base in the northeastern city, located 400 kilometres south of Buenos Aires.

READ MORE: Argentine Navy unsure if satellite calls came from missing submarine

Enrique Balbi, a spokesman for the navy, meanwhile told a press conference in the capital that seven signals received by naval bases over the weekend were not attempted distress calls from the submarine, as previously hoped.

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“We’ve received the report from the company that analyzed the signals — the seven attempted calls did not come from the submarine’s satellite phone,” he said, adding: “We have still been unable to contact them.”

WATCH: What we know so far about Argentina’s missing submarine

1:05 Argentina’s Navy searching for missing submarine with 44 crew on board Argentina’s Navy searching for missing submarine with 44 crew on board

The ARA San Juan, a German-built diesel-electric sub, made its last contact on Wednesday.

A multinational air and sea search is under way with help from countries including Brazil, Britain, Chile, the United States and Uruguay.

False hope?

The submarine’s fate has gripped the nation, with President Argentina Mauricio Macri vowing to find it as soon as possible, as relatives of crew members wait nervously for news in Mar del Plata.

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The navy said Saturday it had received seven calls that day but they did not lock in, an announcement that left many cautiously optimistic they were signs of life from the vessel’s crew.

READ MORE: Satellite signals raise hopes 44 crew on missing Argentine submarine may be alive

On Sunday, a flag was unfurled at the naval base that read: “Be strong Argentina, We trust in God, We wait for you.”

At the Vatican, Argentine-born Pope Francis said he offered “his fervent prayer” for the safety of the submarine sailors.

Multinational rescue efforts

Search efforts meanwhile have been hampered by inclement weather, including a powerful storm that has whipped up waves reaching seven metres in height.

Rescuers are focusing on an ocean patch about 300 kilometres in diameter, radiating from the last point of contact.

WATCH: Argentine submarine goes missing with 44 crew members on board

0:46 Argentine submarine goes missing with 44 crew members on board Argentine submarine goes missing with 44 crew members on board

US Southern Command has deployed a Navy P-8A Poseidon patrol and reconnaissance plane with a crew of 21, along with a NASA P-3 research aircraft, and other equipment and personnel.

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The US Navy has deployed two unmanned underwater vehicles that use a sonar system to create an image of large sections of the sea floor.

Britain’s Royal Navy said it had sent the HMS Protector, an Antarctic patrol ship.

The TR-1700 class submarine had been returning from a routine mission to Ushuaia, near the southernmost tip of South America, to Mar del Plata.

It is one of three submarines in the Argentine fleet.

Sixty-five meters long and seven meters wide, it was built by Germany’s Thyssen Nordseewerke and launched in 1983.

It underwent a refit between 2007 and 2014 to extend its use by about 30 years.