Egyptian Investigators '90 Percent Sure' Russian Airliner Downed by Bomb

The ongoing investigation into the downing of a Russian passenger airliner suggests that the jet suffered "a violent, sudden" end during what would have been an otherwise normal flight over the Sinai Peninsula.

Sources close to the investigation are reportedly growing more convinced that the jet carrying 224 people en route to an Egyptian resort town was downed by a bomb planted in the plane's hold by the Islamic State.

 An anonymous source close to the investigation told the AFP that the circumstance surrounding the crash point to an attack, saying: "Everything was normal during the flight, absolutely normal, and suddenly there was nothing."

A members of Egypt's investigative team told Reuters that they are 90 percent sure, based on audio recordings of the flight, that the plane was downed by a bomb.

"The indications and analysis so far of the sound on the black box indicate it was a bomb," the investigative member, who chose to remain anonymous, told the media outlet. "We are 90 percent sure it was a bomb."

Shortly after the plane crash, members of the Egyptian arm of the Islamic State took responsibility for the crash.

"The fighters of the Islamic State were able to down a Russian plane over Sinai province that was carrying over 220 Russian crusaders. They were all killed, thanks be to God," the terrorist group announced via Twitter.

Russian officials have been hesitant to agree that the Islamic State was behind the recent crash, instead arguing that they must fully complete their investigation without assumptions.