Egyptian investigators say time is running out in the search for the black boxes from an EgyptAir plane that crashed into the Mediterranean last month, killing all 66 people on board.

In a statement Sunday, they say that searches by ships in the area will intensify, given that only around five days remain before the batteries of the flight's data and cockpit voice recorders expire and they stop emitting signals.

The boxes could reveal whether a mechanical fault, a hijacking or a bomb caused the disaster. Finding them without the signals is possible but more difficult.

Since the plane disappeared from radar en route to Cairo from Paris, only small pieces of debris and human remains have been retrieved from the crash site. No group has claimed an attack.