Russian security officials have confirmed that the plane which crashed over Sinai at the end of October was brought down by a bomb, after explosive traces were found on the wreckage.

According to Russian media, security officers believe the bomb was most likely planted inside the hold of the plane by a Sharm el-Sheikh baggage handler.

Egyptian authorities said on Tuesday morning that they had detained two Sharm el-Sheikh airport employees on suspicion of helping to plant a device on the airliner.

Improvised explosives equivalent to 1.5kg of TNT were used to bring the plane down, killing all 224 people on board, the head of Russia's security service, the FSB, has said.

Alexander Bortnikov met with President Vladimir Putin to brief him on the findings of investigators, and according to state media said: "We can definitely say this was an act of terror."

Mr Putin has responded by ordering Russian special forces to "find and punish" those responsible for the crash, and announced a reward of $50m (£33m) for information leading to arrests.

Mr Putin also pledged to increase Russia's military involvement in Syria in response to the news. According to RT, he said: "Our military work in Syria must not only continue. It must be strengthened in such a way so that the terrorists will understand that retribution is inevitable."

The $50m offered represents the highest bounty ever placed on a terrorist or terrorists, and is exactly double the figure placed on the head of al-Qaeda leader Ayman al-Zawahiri by the US.

He said: "We should pursue them without any statute of limitations and should know all of them by name. We will be looking for them wherever they would try to hide. We will find them in any part of the world and punish."

While UK and US intelligence officials have previously pointed to intercepted militant "chatter" suggesting the crash was caused by a bomb, Russia had urged caution until the findings of investigators in Egypt were released.

Russian passenger plane crashes in Egypt Show all 20 1 /20 Russian passenger plane crashes in Egypt Russian passenger plane crashes in Egypt Egyptian soldiers collect personal belongings of plane crash victims at the crash site of a passenger plane bound for St. Petersburg in Russia that crashed in Hassana, Egypt's Sinai Peninsula Russian passenger plane crashes in Egypt Egyptian soldiers collect personal belongings of plane crash victims at the crash site of a passenger plane bound for St. Petersburg in Russia that crashed in Hassana, Egypt's Sinai Peninsula Russian passenger plane crashes in Egypt In this Russian Emergency Situations Ministry photo, made available on Monday, Nov. 2, 2015, showing Metrojet Airbus A321-200 flight 7K9268 flight recorder on display at an undisclosed location in Egypt Russian passenger plane crashes in Egypt Mourners lay flowers at Pulkovo International Airport outside St. Petersburg. Russia on 1 November mourned its biggest ever air disaster after a passenger jet full of Russian tourists crashed in Egypt's Sinai, killing all 224 people on board. Flags were at half mast on the parliament building, in the Kremlin, and on other official buildings in honour of the victims, most of whom were from Russia's second-largest city of Saint Petersburg Russian passenger plane crashes in Egypt People pay their respects at the entrance of Pulkovo airport outside St. Petersburg, during a day of national mourning for the plane crash victims Russian passenger plane crashes in Egypt Debris from the plane crash in Egypt Russian passenger plane crashes in Egypt A piece of an engine of Russian MetroJet Airbus A321 at the site of the crash in Sinai, Russian passenger plane crashes in Egypt The crash site debris Flight 7K9268 crashed in the Sinai peninsula, in all probability killing every one of the 224 people on board AFP/Getty Russian passenger plane crashes in Egypt The crash site debris Debris lies strewn across the sand at the crash site EPA Russian passenger plane crashes in Egypt Relatives in St Petersburg Relatives react after a Russian airliner with 217 passengers and seven crew aboard crashed, as people gather at the Kogalymaviaís information desk at Pulkovo airport in St Petersburg on 31 October AP Russian passenger plane crashes in Egypt Relatives in St Petersburg A relative of a passenger of MetroJet Airbus A321 at Pulkovo II international airport in St Petersburg, Russia, 31 October 2015. EPA Russian passenger plane crashes in Egypt The plane's journey The plane's last recorded radar position above the northern Sinai peninsula Flightradar24 Russian passenger plane crashes in Egypt Where it crashed A satellite view from Google Maps of the rough area where the plane crashed, in the mountainous Hassana region of the Sinai peninsula. Google Maps Russian passenger plane crashes in Egypt The plane The Metrojet's Airbus A-321 with registration number EI-ETJ that crashed in Egypt's Sinai peninsula REUTERS/Kim Philipp Piskol Russian passenger plane crashes in Egypt The plane The crashed Airbus A321 at Domodedovo international airport, outside Moscow,, on 20 October Russian passenger plane crashes in Egypt Relatives at in St Petersburg A relative of a passenger on MetroJet Airbus A321 at Pulkovo II international airport in St Petersburg EPA Russian passenger plane crashes in Egypt Relatives at in St Petersburg Relatives of passengers of MetroJet Airbus A321 at the Crown Plaza hotel in St Petersburg EPA Russian passenger plane crashes in Egypt Bodies being repatriated An Egyptian soldier prays as emergency workers prepare to unload bodies of victims from a police helicopter to ambulances at Kabrit military airport on 31 October. AP Russian passenger plane crashes in Egypt Bodies being repatriated Ambulances line up as emergency workers unload bodies at Kabrit military airport, 20 miles north of Suez, on Saturday AP Russian passenger plane crashes in Egypt Bodies being repatriated Egyptian paramedics load the corpses of victims into a military plane at Kabrit military air base by the Suez Canal on October 31, 2015 AFP/Getty Images

The discovery of explosive traces on the wreckage represents the first concrete evidence from the crash site itself that a bomb was used. According to Mr Bortnikov, experts analysed personal items belonging to passengers as well as parts of the plane itself.

The Isis militant group has claimed responsibility for bringing down the Airbus A321 jet, which was on route from Sharm el-Sheikh to St Petersburg when it crashed on 31 October.

Egypt: Russian crash investigators search Sinai for victims' belongings

In video, audio and written statements, Isis claimed the attack was retaliation for Russia's military campaign in Syria, and challenged investigators to "prove we did not do it".