Egypt has sent a submarine to search for the black boxes of the crashed EgyptAir Airbus A320, the country’s President Abdul Fattah al-Sisi has said.

"We are moving hard to retrieve the two boxes," the Egyptian President said in a televised address on Sunday which was his first public comments on the crash, the BBC reported.

The Egyptian underwater search equipment from Egypt's offshore oil industry can operate at a depth of 3,000 metres below surface, according to al-Sisi.

There are conflicting reports as to whether search crews have already located the black boxes - voice and flight data recorders of the aircraft - in the Mediterranean.

EgyptAir Flight MS804 carrying 66 passengers and crew crashed in the Mediterranean some 290 km from the Egyptian port city of Alexandria early Thursday en route to Cairo from Paris with no obvious explanation. According to investigators quoted by international newswires, smoke was detected in the cabin of the aircraft three minutes before it disappeared from radar screens.

The cause of the crash remains a mystery but Egypt's civil aviation minister has said the possibility of a terror attack was stronger than technical failure.