The Russian airliner that crashed in Egypt’s Sinai region Saturday suffered a “violent, sudden” demise, data recovered from one of the two black boxes showed, according to a source involved in the investigation in Paris, reported Agence France-Presse. The flight data recorder seemed to indicate that “everything was normal during the flight, absolutely normal, and suddenly there was nothing.”

The reported revelation was seen to lend weight to speculation that an explosive device could have brought down Airbus A321m. Militants aligned with an Egyptian affiliate of the Islamic State group, also known as ISIS, immediately took responsibility for the attack, but Egypt’s president has labeled their claims “propaganda.”

Several theories have been postulated for what may have happened to the airline, but officials have expressed increasing conviction that an explosive device may have been on board. British, Irish and Russian airlines have canceled flights to the region amid security concerns and are working to bring home citizens still at the Sharm el-Sheikh resort. An investigation into the crash, which killed all 224 people on board, continues.

Investigators first extracted content from one of the two black boxes Wednesday. Although little information has yet been made public about what the data recorder may have revealed, early local press reports indicated that it picked up abnormal sounds before the crash. A second black box with audio from the cockpit was partially damaged and was expected to require extra time to extract and validate the data.

Russia intervened in Syria in late September in the hope of bolstering Syrian President Bashar Assad. ISIS has repeatedly made threats to target Russian interests in response to the country's campaign in Syria. ISIS released a video from one of its strongholds in Iraq celebrating the attacks Wednesday, brandishing smiles and bowls of candy for passersby. At the end of the video, insisting they were responsible for the attack, militants threatened further terrorism against Russia.