Egypt's Prosecutor-General Nabil Sadek referred on Thursday investigations into the deadly crash of a Russian airliner last October in Sinai to the Supreme State Security Prosecution, a statement by the prosecutor's office said. 

In March, an official Russian investigation report, which said that criminal activity was behind the deadly crash of the Metrojet airliner that killed all 224 on board, was delivered to Egyptian authorities.

Egypt's Supreme State Security Prosecution (SSP) prosecutes crimes related to terrorism and national security. 

The Kremlin had said as early as 17 November 2015 that a bomb ripped apart the Russian passenger jet and promised to hunt down those responsible.

Prior to Thursday's decision to refer the case to the SSP, Egyptian prosecutors did not produce any final report on the cause of the crash.

However, last February, President Abdel-Fattah El-Sisi hinted in public remarks that a terror attack might have downed the Russian plane.

The Islamic State militant group has claimed responsibility of the deadly attack. 

Following the crash, Russia and several other European countries suspended direct flights to Egypt, citing concerns over security conditions in Egyptian airports, with Russia demanding improved security measures before it resumes flights to Egypt.

Egypt and Russia have repeatedly said the two countries would make joint efforts to resume direct flights as soon as possible.