There are no facts indicating that Sunday’s crash of the Russian Defense Ministry’s Tu-154 plane off the Sochi coast was a terrorist attack, the Federal Security Service told.

Axar.az reports citing to TASS news agency.

"We have got no signs or facts indicating that an act of terrorism or sabotage was committed onboard," the FSB said.

FSB said the investigators probing into the causes of the crash are proceeding along four main lines of inquiry.

"The four main versions are an engine being hit by a foreign object, substandard fuel that caused the loss of thrust on and eventually stopped the engines, the pilot’s mistake and the plane’s technical failure," the FSB said.

"By now several witnesses of the plane’s crash have been established. Also, there is a file retrieved from a car video recorder. The investigators are questioning the witnesses and examining the video," the FSB said.

A Tupolev-154 passenger jet of the Russian Defense Ministry was on the way to Latakia, Syria. On December 25 it went missing from the radar screens at 05:25 Moscow time, a minute after leaving Sochi airport, at a distance of 6,250 meters from the edge of the runway. Radio contact with the plane was instantly lost.

At this point it is already clear that the plane’s speed at the moment of takeoff was 345 kilometers per hour, which is a standard speed for the planes of this type. The site of the crash has been identified 1,500 meters away from the coastline. A massive search operation is proceeding in the area.