A French naval ship has picked up signals believed to be from the black boxes of the EgyptAir plane that crashed into the Mediterranean last month, killing all 66 people on board.

The vessel picked up the signals from the seabed of the wreckage search area that is “assumed to be from one of the data recorders“, Egypt’s ministry of civil aviation said on Wednesday, citing the investigation committee.

Locator pings emitted by flight data and cockpit voice recorders, known as the black boxes, can be picked up from deep underwater.

Another vessel, the John Lethbridge, from the Deep Ocean Search will join the search team within a week to retrieve the boxes, the ministry said.

The Airbus A320 had been cruising normally in clear skies on a nighttime flight to from Paris to Cairo early on May 19 when it suddenly lurched left, then right, spinning all the way around and plummeting more than 11,500 metres into the sea.

Since the crash, small pieces of the wreckage and human remains have been recovered while the bulk of the plane and the bodies of the passengers are believed to be deep under the sea.

A Cairo forensic team has received the human remains and is carrying DNA tests to identify the victims.

The search has narrowed down to a 5-kilometer area in the Mediterranean.

David Learmount, a consulting editor at the aviation news website Flightglobal, said the black boxes’ batteries can transmit signals up to 30 days after the crash. But even if the batteries expire, locating the boxes remains a possibility.

“It’s terribly important to find the black boxes, because if they don’t find them, they will know nothing about the aircraft,” he said, citing a 2009 incident when black boxes were found two years after a crash in the Atlantic Ocean.

Nearly two weeks after the crash off Egypt’s northern coast, the cause of the tragedy still has not been determined.

Egypt’s civil aviation minister Sherif Fathi has said he believes terrorism is a more likely explanation than equipment failure or some other catastrophic event.

But no hard evidence has emerged on the cause, and no militant group has claimed to have downed the jet. Earlier, leaked flight data indicated a sensor had detected smoke in a lavatory and a fault in two of the plane’s cockpit windows in the final moments of the flight.