Russia's security chief said a passenger plane that crashed in Sinai, Egypt, with 224 people on board was brought down in a "terrorist attack."

Russian Federal Security Service (FSB) chief Alexander Bortnikov said remnants of explosives were discovered in the debris of the plane, leading Russian investigators to conclude it had been blown up by an explosive device.

"According to our experts, a homemade explosive device equivalent to 1 kilogram of TNT went off onboard, which caused the plane to break up in the air, which explains why the fuselage was scattered over such a large territory. I can certainly say that this was a terrorist act," Bortnikov said in a meeting with Russian President Vladimir Putin on Monday night.

Reuters reported two Sharm el Sheikh airport employees are being held over accusations they assisted in the planting of bombs on the flight. The Egypt Independent reported the Interior Ministry denied the claims in the Reuters report.

Putin has vowed to do whatever it takes to find and punish all those behind the bombing.

"There's no statute of limitations for this, we need to know all of their names," Putin said. "We're going to look for them everywhere wherever they are hiding. We will find them in any place on Earth and punish them."

The Russian Metrojet Airbus A321-200 was flying to St. Petersburg from Egyptian resort destination Sharm El-Sheikh when it crashed Oct. 31. The plane was carrying 217 passengers and seven crew members, and there were no survivors.

The announcement follows weeks of speculation about what caused the crash, with UK and U.S. investigators asserting on Nov. 5 that a bomb was behind the disaster. Due to security concerns, flights were cancelled to the region.

Investigators look at the wreckage of the crashed plane. Image: Getty Images

On Nov. 7, Putin followed the lead of the UK and halted flights from Russia to Egypt, at the advice of his intelligence staff. It followed the UK sharing their intelligence with him, Putin said recently.

Islamic State has claimed responsibility for bringing the Russian plane down in written statements, as well as video and audio messages posted on the Internet following the crash.

It said the attack was retaliation for Russia's air campaign against IS — and other groups — in Syria, where Moscow wants to preserve the rule of President Bashar Assad. The group did not offer any details to back its claim.

While releasing specifics would add credibility, the group may be withholding either because its claim is false, or because doing so would undermine plans for similar attacks in the future — or because the aura of mystery might deepen its mystique among die-hard followers.

IS has also claimed responsibility for Friday attacks in Paris that killed 129 people and wounded 350 others.



— Additional reporting by the Associated Press