Police open the way for ambulances carrying the bodies of passengers of a Russian airliner which crashed in Sinai, into a morgue in Cairo, Egypt, October 31, 2015. Of the 224 passengers and crew members on board, 129 bodies have been picked up.[Photo/Agencies]

Egyptian Prime Minister Sherif Ismail said on Saturday no "irregular" activities were believed to be behind a Russian Airbus-321 plane that crashed in Egypt's Sinai earlier on Saturday.

"The black box is what will determine the reason for the plane crash," Ismail added.

A claim by a group allied to the so-called Islamic State (IS) in Sinai that it brought down the plane has been dismissed by both Russia and Egypt.

"Experts asserted that a plane flying that high technically cannot be shot down," the Egyptian prime minister answered one of the reporters, stressing there was nothing "irregular" behind the accident.

There have been media reports that the group loyal to the IS, have acquired Russian shoulder-fired, anti-aircraft missiles.

But these types of missiles can only be effective against low-flying aircraft or helicopters.

The Russian airliner was cruising at 31,000 feet when it lost contact with air traffic controllers, according to Egyptian aviation officials.

Bodies, black boxes retrieved

Egypt has already found and obtained both black boxes from the crashed Russian passenger plane, the civil aviation minister told a news conference.

There are normally two black boxes on an aircraft, one for cockpit voice recordings and one for flight data. Egyptian authorities had earlier said they only found one.

Of the 224 passengers and crew members on board, 129 bodies have been picked up.

The plane crashed in North Sinai province and all its passengers, mostly Russians, died in the tragic accident.

Ismail told reporters that around 50 ambulances hurried to the scene and that the dead bodies are currently being transferred to Zeinhom Morgue in the capital Cairo.

The aviation ministry said the wreckage was found in Hassana, a mountainous area 35 km south of Arish city.