Egypt air navigation official says plane did not swerve or lose altitude before it disappeared, as claimed by Greece.

The head of Egypt's state-run provider of air navigation services says that EgyptAir flight 804 did not swerve or lose altitude before it disappeared off radar, challenging an earlier account by Greece's defence minister.

Ehab Azmy, head of the National Air Navigation Services Company, told The Associated Press news agency on Monday that in the minutes before the plane disappeared it was flying at its normal altitude of 37,000 feet, according to the radar reading.

He said: "That fact degrades what the Greeks are saying about aircraft suddenly losing altitude before it vanished from radar."

According to Greece's defence minister Panos Kammenos, the plane swerved and dropped to 10,000 feet before it fell off radar.

Greek civil aviation authorities say all appeared fine with the flight until air traffic controllers were to hand it over to their Egyptian counterparts.

Meanwhile the search for the plane, which crashed with 66 aboard on Thursday, continues, with French navy ships arriving in the Mediterranean Sea on Monday.

The 10 crew and 56 passengers included 30 Egyptian and 15 French nationals.

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The vessel is equipped with sonar that can pick up the underwater "pings" emitted by the recorders. It is specialised in maritime surveillance, and rescue and marine police missions.

Moreover, teams searching for the black box flight recorders have been facing technical constraints.

Air crash investigation experts say the search teams have around 30 days until the batteries die to listen for pings sent out once every second from beacons attached to the two black boxes, as they scour 17,000 square kilometres of sea north of the Egyptian port city of Alexandria.

At this stage of the search, they would typically use acoustic hydrophones, bringing in more advanced robots later to scan the seabed and retrieve any objects once they have been found.

French investigators say the Egyptian jet sent warnings indicating that smoke was detected on board. The signals did not indicate what caused the smoke, and aviation experts have not ruled out deliberate sabotage or a technical fault.

Ships and planes scouring the sea have found body parts, personal belongings and debris from the Airbus 320, but are still trying to locate the black box recorders that could shed light on the cause of the crash.

The search for EgyptAir's Airbus A320 is especially challenging because its wreckage lies in one of the deepest parts of the Mediterranean, at a depth of 2,000-3,000 metres, which is on the edge of the range for hearing pinger signals.

The search for EgyptAir is especially challenging because its wreckage lies in one of the deepest parts of the Mediterranean