CAIRO/PARIS, June 1 -- A French search vessel has picked up signals from one of the black boxes of EgyptAir flight MS804, Egyptian and French investigators said, a potential breakthrough in efforts to uncover why it plummeted into the Mediterranean last month.

Search teams are working against the clock to recover the two flight recorders that will offer vital clues to the fate of the plane that crashed en route from Paris to Cairo on May 19 killing all 66 people on board.

Without the black boxes, say investigators and aviation disaster experts, there is not enough information to determine what went wrong or whether the plane was brought down deliberately.

The recorders are designed to emit acoustic signals for 30 days after a crash, giving search teams fewer than three weeks to spot them in waters up to 9,840-feet (3,000 meters) deep, which is on the edge of their range.

The Egyptian investigation committee said on Wednesday that the search was intensifying ahead of the arrival of another vessel, the John Lethbridge, from Mauritius-based company Deep Ocean Search to help retrieve the devices. That ship is expected to arrive within a week, it said.

"Search equipment aboard French naval vessel Laplace ... has detected signals from the seabed of the search area, which likely belong to one of the data boxes," the Egyptian committee said in its statement.

France's aviation accident bureau BEA confirmed that the signal had come from one of the recorders.

The Laplace has equipment from ALSEAMAR, a subsidiary of French industrial group Alcen, which can pick up black box pinger signals over long distances up to 5 km (3 miles) and was contracted by the Egyptian investigators last week.

Egyptian investigators have said that the EgyptAir plane did not show any technical problems before taking off and the pilot made no distress call to air traffic control.

There has been no claim of responsibility for the crash.

The jet transmitted a series of messages in the minutes before it crashed showing a rise in temperature at the co-pilot's window and smoke on board, but investigators say these shed little light on the cause.

There are also conflicting reports of the plane's last moments as it crossed from Greek to Egyptian airspace.

The head of Egypt's air navigation has told Reuters the plane disappeared suddenly from the radar while at a cruising altitude of about 37,000 feet.

That conflicts with the account given on the day of the crash by the Greek defence minister, who said the plane swerved and dropped to 15,000 feet before disappearing from radar.

The air disaster is the latest in a series for Egypt, complicating its efforts to restore tourism, which has suffered since the 2011 uprising ushered in a period of instability.

In March, a man wearing a fake suicide belt hijacked an EgyptAir flight. In late October, a Russian plane carrying holidaymakers from a Red Sea resort crashed in Sinai.

Islamic State said it downed the plane with a bomb. Britain and Russia suspended flights to Sharm al-Sheikh pending improvements to security.