Egyptian authorities arrested two airport staff in connection with the Metrojet plane that crashed over the Sinai last month, killing 224 people, as the head of Russia's FSB security service on Tuesday told Russian President Vladimir Putin that it's now clear a homemade explosive device brought down aircraft and that the bombing was a "terrorist" act.

Two security officials and an airport employee at Sharm El-Sheikh airport told Reuters that Egyptian authorities had detained two members of the ground crew for questioning, days after Egypt had launched an investigation about a possible crew role in the attack. One of the security officials said CCTV footage showed a baggage handler carrying a suitcase from an airport building to another man, who was loading luggage onto the doomed airliner from beneath the plane on the runway.

The detentions came as Alexander Bortnikov, the head of the Russian FSB, determined that “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.” Bortnikov added, “I can certainly say that this was a terrorist act.”

The Islamic State in Iraq and the Levant (ISIL) 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.

All of the people on board, most of them Russian tourists, were killed when the Metrojet Airbus A321 crashed over the Sinai Peninsula on Oct. 31, about 23 minutes after taking off from the Red Sea resort city of Sharm El-Sheikh. The plane was headed to St. Petersburg, where most of the passengers were from.

The FSB later appealed to “Russian and international communities for cooperation in identifying the terrorists“ and offered “50 million U.S. dollars” reward.

Egypt had resisted British and U.S. assertions that an explosive device was the likely cause of the Russian plane's crash. Later, government officials and the pro-government media shifted their focus away from the cause of the crash to speculating on what they called a Western conspiracy against Egypt and the crushing impact of the crash on the country's vital tourism industry.

The Sinai Province of Egypt, where the airport is located, is home to ISIL's Egyptian affiliate, which has carried out attacks against Egyptian security forces and officials. Observers have suggested that the group may have taken advantage of lax security at the airport, or used an insider to place the explosive.

Meanwhile, 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.”

ISIL said the attack was retaliation for Russia's air campaign against it and other groups in Syria, where Moscow wants to preserve the rule of Syrian President Bashar al-Assad.

Putin said Tuesday that Russia's air campaign in Syria “should not only be continued but should be intensified so that the criminals realize that retribution is inevitable.”

He instructed the Defense Ministry and General Staff to present their suggestions on how Russia's operation in Syria could be modified.

“In this work, including the search to find and punish the criminals, we are relying on all of our friends,“ Putin said.

“We will act in accordance with the U.N. Charter's Article 51, which gives each country the right to self-defense. Everyone who tries to aid the criminals should understand that they will be responsible for giving them shelter.”

Russia made the announcement the day after meetings with other world leaders in Turkey, where they vowed to work together to combat ISIL group.

ISIL has warned Putin that it would also target him “at home,” but did not offer any details to back its claim.

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

Al Jazeera and wire services