A homemade explosive device brought down a Russian passenger plane over Egypt last month, the head of Russia's FSB security service said Tuesday, November 17, telling Russian President Vladimir Putin it's now clear the bombing that killed 224 people was a terrorist act, the Associated Press reports.

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

"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," FSB head Alexander Bortnikov said.

He said tests showed the explosives had been produced outside of Russia, but gave no further details.

In Cairo, there was no immediate comment on the news from the Egyptian government. State-owned television carried the newsbreak from Moscow, but had no official comment either.

Putin vowed to hunt down those responsible for the attack.

"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 Islamic State group 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.