Hopes have been raised for a missing Argentinian submarine after the country's Navy said it detected noises that could lead them to the stricken vessel.
The ARA San Juan vanished last Wednesday after it radioed commanders to report a fault while sailing from Ushuaia, in the country's south, to Mar del Plata, near Buenos Aires.
But two ships picked up sonar signals that could have been made by crew members knocking on the sub's hull with tools, CNN reported.
The Navy is now analysing the signals to see if they are genuine, after previous transmissions which were thought to be distress signals turned out to be bogus, according to the Daily Mail.
Earlier, Enrique Balbi, a spokesman for the Navy, said analysis of radio transmission received over the weekend revealed that "the seven attempted calls did not come from the submarine's satellite phone".
"We have still been unable to contact [the submarine]," he added.
A multinational air and sea search is under way with help from countries including Brazil, Britain, Chile, the United States and Uruguay.
Storms have complicated efforts to find the sub, which had gone missing in the South Atlantic.
Authorities have mainly been scanning the sea from above, as storms have made the search difficult for boats.
The Royal Navy has deployed the HSM Protector, a polar exploration vessel, to the southern Argentine Sea to assist in searches.
Britain and Argentina fought a war in 1982 over the Falklands Islands, which are called the Malvinas in Argentina.
A spokesman for the British Navy said: "Following a request from the Argentine Government, HMS Protector has been deployed to join the search and rescue effort for the ARA San Juan."
The US Navy ordered its Undersea Rescue Command based in San Diego, California, to deploy to Argentina to support the search for the submarine.
The country's first female submarine officer, 35-year-old Eliana Krawczyk, is among the 44 crew missing after the vessel lost contact more than 402km from the coast.
A multi-national rescue operation has been launched to find Krawczyk and her crewmates, including an aircraft from Nasa.
President Mauricio Macri said in a tweet that the country will use "all resources national and international that are necessary to find the submarine".
Relatives of the crew members gathered at the Mar del Plata Naval Base in the hopes of hearing news about their loved ones.
"We feel anguish. We are reserved but will not lose our hope that they will return," Marcela Moyano, wife of machinist Hernan Rodriguez, told television network TN.
"We're very worried, we have little news, we're waiting for communication," said Eduardo Krawczyk.
From the Vatican, Pope Francis, an Argentinian, said he was saying "fervent prayers" for the crew.
The TR-1700 class diesel electric submarine had been returning from a routine mission to its base at Mar del Plata, around 402km south of Buenos Aires.
The San Juan is one of three submarines in the Argentine fleet.
The 213-foot long submarine, which uses diesel-electric propulsion, was built in 1983 by Germany's Thyssen Nordseewerke. However, it underwent a seven-year refit between 2007 and 2014 to extend its life by a further 30 years.
The Navy believes the submarine had communication difficulties that may have been caused by an electrical outage.
Navy protocol would call for the submarine to come to the surface once communication was lost.
Balbi said: "We expect that it is on the surface."