MAR DEL PLATA, Argentina (Reuters) – The Argentine navy raised the possibility on Thursday that a navy submarine missing in the South Atlantic suffered an explosion, heightening concerns over the fate of the 44 crew members.

An abnormal sound detected underwater by an international agency on the morning of Nov. 15, around the time that the ARA San Juan sent its last signal and in the same area, was “consistent with an explosion,” navy spokesman Enrique Balbi told reporters.

The navy did not have enough information to say what the cause of the explosion could have been or whether the vessel might have been attacked, Balbi said.

He was commenting on information the navy received on Thursday from the Comprehensive nuclear Test-Ban Treaty Organization (CTBTO), an international body that runs a global network of listening posts designed to check for secret atomic blasts.

The Vienna-based agency, which has monitoring stations equipped with devices including underwater microphones that scan the oceans for sound waves, said in a statement that two of its stations had detected an unusual signal near where the submarine went missing. But the agency was more guarded about whether this was caused by an explosion.

A huge sea and air hunt is being conducted for the San Juan, a German-built, diesel-electric powered submarine that was launched in 1983, as crew members’ relatives wait anxiously for news more than a week after the vessel disappeared.

The relatives, camped out in a naval base in the coastal city of Mar del Plata, have been largely optimistic until now, but they shed tears and insulted authorities after being briefed on the news of the possible explosion. They were told about it before the public announcement.

Balbi said that the news of the abnormal sound was consistent with a separate report received Wednesday of an “acoustic anomaly” in the same area and around the same time. The San Juan was some 430 km (270 miles) off the Patagonian coast when it sent its last signal.

“This is very important because it allows us to correlate and confirm the acoustic anomaly from the U.S. report yesterday,” Balbi said. “Here, we’re talking about a singular, short, violent, non-nuclear event, consistent with an explosion.”

In Vienna, CTBTO hydroacoustic engineer Mario Zampolli said the signal his agency had detected, “could be consistent with an explosion but there is no certainty about this.” Speaking to Reuters, he agreed with Balbi’s description of the signal as unusual and short, adding that the cause was non-natural.

The submarine was en route from Ushuaia, the southernmost city in the world, to Mar del Plata, some 400 km (250 miles) south of Buenos Aires, when it reported an electrical malfunction shortly before disappearing.

The vessel had seven days of oxygen supply, meaning the crew would be running low if it had not been able to surface.

HOPE FADING

The news of the possible explosion prompted some family members to fear the worst, and many criticized the authorities’ response to the crisis.

“They kept us here for a week. Why did they not tell us?” Itati Leguizamon, the wife of a crew member. “I do not have any more hope, it is over.”

Some relatives have questioned authorities for letting the crew navigate on an aging submarine – criticism that has highlighted the armed forces’ dwindling resources since the end of a military dictatorship in the 1980s.

Authorities have said the level of maintenance, not the age, was what mattered, and that the vessel was in good condition. It received a major mid-life upgrade in 2009, in which its four diesel engines and electric propeller engines were replaced, according to specialist publication Jane’s Sentinel.

Earlier on Thursday, a U.S. embassy spokeswoman said an object detected by a U.S. Navy plane near the area where the submarine sent its last signal turned out not to be the missing vessel. The plane, a P-8A Poseidon, was one of dozens of Argentine and foreign boats and planes involved in the hunt.