A search was underway Friday for an Argentine submarine with 44 crew members on board after the craft went missing. The ARA San Juan, a military submarine, gave its last location Wednesday when it was in the southern Argentine Sea.

The submarine was last seen off the coast of Puerto Madryn in southern Argentina, where the navy was conducting an exercise, according to Argentine media reports. It had previously left the southern city of Ushuaia to head toward Mar del Plata naval base.

Officials were investigating the possibility of a communication failure, according to Reuters. The submarine was equipped with enough food to continue on its journey to Mar del Plata regardless of whether there were communication problems, authorities said.

“We are investigating the reasons for the lack of communication,” said Enrique Balbi, a naval spokesman, according to Reuters. “If there was a communication problem, the boat would have come to the surface.”

Initial reports indicated there may have been a power outage on the ship and potentially a fire, according to Naval Today. And while some reports stated the submarine had been found and was being towed to Mar del Plata, a naval spokesperson said that was not true.

The ARA San Juan is a diesel-electric submarine that was first put into use in 1985, according to Naval Today. After being repaired for a number of years, the submarine was put back into service in 2014.

“The last reliable and official information is that the submarine has not yet been found,” Balbi said, according to the Defense Post. “It is not that it is lost, to be lost you have to look for it and not find it.”

The Argentine navy had not yet issued an official statement regarding the submarine.