A storm on Sunday complicated the search for an Argentine navy submarine missing in the South Atlantic with 44 crew members on board.
Authorities were also attempting to verify that recent satellite calls seen as a sign the sailors were alive came from the vessel.
US planes carrying subsurface search specialists arrived in Argentina to help hunt for the ARA San Juan, which was 432km (268 miles) off Argentina's coast when its location was last known early on Wednesday, said navy Admiral Gabriel Gonzalez.
More than a dozen boats and aircraft from Argentina, the US, Britain, Chile and Brazil had joined the effort.
Authorities have mainly been scanning the sea from above as waves of up to 8m (26 ft) and winds of up to 40 knots made the search difficult for boats, Admiral Gonzalez told reporters.
"Unfortunately these conditions are expected to remain for the next 48 hours," Admiral Gonzalez said from the Mar del Plata naval base, about 420km (240 miles) south of Buenos Aires where the submarine had been heading toward before vanishing.
The defence ministry has said the submarine appeared to have tried to make contact through seven failed satellite calls on Saturday between late morning and early afternoon. On Sunday afternoon, Admiral Gonzalez said it was still not clear whether the calls were sent by or to the vessel.
"What we are trying to do today is geolocate those calls to see if they correlate with any point in the operation zone that would suggest it is the San Juan submarine," navy spokesman Enrique Balbi told reporters on Sunday afternoon.
The government was working with Iridium Communications Inc to trace the location of the calls.
A search of 80 per cent of the area initially targeted for the operation turned up no sign of the submarine on the ocean’s surface, but the crew should have ample supplies of food and oxygen, Mr Balbi said.
The navy said an electrical outage on the diesel-electric-propelled vessel might have downed its communications. Protocol calls for submarines to surface if communication is lost.
Three boats left Mar del Plata on Saturday with radar detection probes and were following the path that the submarine would have taken to arrive at the base in reverse, Mr Balbi said.
“Those probes allow the boats to sweep the ocean floor during their journey and try to make a record of the floor in three dimensions,” Mr Balbi said.
The US navy said its four aircraft were carrying a submarine rescue chamber designed during the second World War that could reach a bottomed submarine at depths of 850ft and rescue up to six people at a time. The chamber can seal over the submarine’s hatch to allow sailors to move between the vessels.
It said it also brought a remote-controlled vehicle that could be submerged and controlled from the surface
Messages
Crew members' relatives gathered at the Mar del Plata naval base, where the submarine had once been expected to arrive around noon on Sunday from Ushuaia. However, it would not be unusual for storms to cause delays, Mr Balbi said.
At the entrance of the base, locals hung signs with messages in support of the crew members and their families on a chain-link fence.
“Strength for Argentina. We trust in God. We are waiting for you,” read a message inscribed on an Argentine flag hanging on the fence.
“Let’s go, men of steel. We are waiting for you at home,” read a message written on a picture of the submarine.
Argentine-born Pope Francis mentioned the missing vessel in his Sunday noon prayer.
“I also pray for the men of the crew of the Argentine military submarine which is missing,” the pontiff said. – Reuters