(CNN) The Russian passenger jet that crashed over Sinai, Egypt, was brought down by a bomb estimated to contain 1 kilogram (2.2 pounds) of explosives, the head of the Russian Federal Security Service said Tuesday, and the Russian government is offering a $50 million reward for information about those who brought it down.

The government had initially resisted the theory that the plane fell victim to terrorism, perhaps in retaliation for Russia's support of the government of Bashar al-Assad in Syria.

But in a turnaround, the government is offering the reward, according to the official Sputnik news.

An Egyptian soldier prays as emergency workers prepare to unload bodies of victims at a military airport north of Suez, Egypt, on October 31.

An Egyptian soldier prays as emergency workers prepare to unload bodies of victims at a military airport north of Suez, Egypt, on October 31.

Journalists and spectators wait for ambulances to arrive at the Zeinhom morgue in Cairo on October 31.

Journalists and spectators wait for ambulances to arrive at the Zeinhom morgue in Cairo on October 31.

Employees with the Russian Ministry for Emergency Situations wait in Moscow for their flight to Egypt on October 31.

Employees with the Russian Ministry for Emergency Situations wait in Moscow for their flight to Egypt on October 31.

People light candles and leave flowers at the Russian Embassy in Kiev, Ukraine, on October 31.

People light candles and leave flowers at the Russian Embassy in Kiev, Ukraine, on October 31.

Villagers watch an ambulance as it drives to unload bodies on October 31.

Villagers watch an ambulance as it drives to unload bodies on October 31.

The tail of the jet sits in a field on October 31.

The tail of the jet sits in a field on October 31.

An item of clothing lies at the site where the plane crashed on October 31.

An item of clothing lies at the site where the plane crashed on October 31.

Ismail, center, and other officials visit the site of the plane crash on October 31.

Ismail, center, and other officials visit the site of the plane crash on October 31.

Egyptian Prime Minister Sherif Ismail, third from right, visits the site of the plane crash with military and government officials on October 31.

Egyptian Prime Minister Sherif Ismail, third from right, visits the site of the plane crash with military and government officials on October 31.

Egyptian paramedics load the bodies of victims into a military plane at a military air base by the Suez Canal on Saturday, October 31.

Egyptian paramedics load the bodies of victims into a military plane at a military air base by the Suez Canal on Saturday, October 31.

People place flowers and messages in front of the Russian Embassy in Cairo on November 1.

People place flowers and messages in front of the Russian Embassy in Cairo on November 1.

Candles, toys, flowers and portraits are left at Pulkovo International Airport outside St. Petersburg on November 1.

Candles, toys, flowers and portraits are left at Pulkovo International Airport outside St. Petersburg on November 1.

Debris from the airliner is seen on November 1.

Debris from the airliner is seen on November 1.

More debris is shown on November 1. The crash site is in a remote area of a region plagued by a violent Islamic insurgency.

More debris is shown on November 1. The crash site is in a remote area of a region plagued by a violent Islamic insurgency.

Debris belonging to the Russian airliner is shown at the site of the crash on November 1.

Debris belonging to the Russian airliner is shown at the site of the crash on November 1.

Egyptian army soldiers guard the luggage and other belongings of passengers piled up at the site of the crash on November 1.

Egyptian army soldiers guard the luggage and other belongings of passengers piled up at the site of the crash on November 1.

A piece of the engine sits on the ground at the crash site on November 1.

A piece of the engine sits on the ground at the crash site on November 1.

Egyptian military personnel stand near the tail of the jet in Hassana on Sunday, November 1.

Egyptian military personnel stand near the tail of the jet in Hassana on Sunday, November 1.

Russian emergency personnel collect personal belongings of victims at the crash site in Hassana, Egypt, on November 2.

Russian emergency personnel collect personal belongings of victims at the crash site in Hassana, Egypt, on November 2.

The wreckage of Flight 9268 is seen in this image provided on Tuesday, November 3.

The wreckage of Flight 9268 is seen in this image provided on Tuesday, November 3.

The militant group ISIS published this image of what it claims is the bomb that brought down Metrojet Flight 9268 on Saturday, October 31. The photograph shows a soft-drink can and two components that appear to be a detonator and a switch. Flight 9268 crashed in Egypt's Sinai Peninsula en route to the Russian city of St. Petersburg. All 224 people on board were killed.

Also on Tuesday, a U.S. defense official said Russia had conducted a "significant number of strikes" in Raqqa in northern Syria in the past several hours. The terrorist group ISIS , which has claimed responsibility for downing the plane, has made its Syrian headquarters in Raqqa.

The group's claim has yet to be verified. It has also claimed responsibility for the massive terrorist attack in France on Friday, in which at least 129 people were killed.

Putin: 'We remember everything'

The head of the FSB, Aleksandr Bortnikov, said the homemade bomb had the explosive power of one kilogram of TNT, according to the Kremlin.

A girl cries during a funeral this month for Nina Lushchenko, 60, a victim of the Metrojet crash.

The remarks came in a meeting Russian President Vladimir Putin held with various security and foreign affairs officials -- a meeting that began with a minute of silence for the victims of the crash.

The bomb, Bortnikov told Putin, explained why fragments of the plane were scattered over a large area, the Kremlin website said.

"This is not the first time Russia experiences barbaric terrorist crime, usually without any obvious internal or external causes, the way it was with the explosion at the railway station in Volgograd at the end of 2013." Putin said. "We remember everything and everyone."

He said Russians would not dry their tears, but would nevertheless find and punish those responsible.

"We have to do it without any period of limitation; we need to know all their names," Putin said. "We will search wherever they may be hiding. We will find them anywhere on the planet and punish them."

He told the Foreign Ministry to appeal for international help.

'Security has got to be enhanced'

Western governments, particularly those in Britain and the United States, had said they had information pointing to a bomb having brought the plane down, and have said it may have been smuggled aboard the plane in Sharm el-Sheikh, from which the plane took off -- possibly with help from an airport employee.

Crash victims Leonid Gordin and Alexandra Illarionova had been on a romantic break in Sharm el-Sheikh. Gordin may have proposed on their Egyptian vacation.

They have criticized security procedures at the airport at Sharm el-Sheikh. The plane was bound for St. Petersburg, Russia.

Reuters, citing security officials, reported Tuesday that two Sharm el-Sheikh airport employees had been detained in connection with the Metrojet investigation. But Egyptian authorities denied the report.

Both a spokesman in Egypt's Interior Ministry and a spokesman in Egypt's Civil Aviation Ministry denied to CNN that any arrests have been made in connection to the crashed plane.

CNN spoke Tuesday with Carolyn McCall, chief executive of the UK budget airline EasyJet, who has called for aviation security and regulation to be improved.

A photo of one of the youngest victims on the crash went viral. It shows 10-month old Darina Gromova looking out the window at the St. Petersburg Airport on October 15.

"The reason the British government advised all airlines to stop flying to Sharm is that they believed there was a device in the hold of the Metrojet aircraft," McCall said. "They had inside intelligence giving them that information, so that's not surprising to anybody in the airline industry, given that the British government took very strong action immediately. Clearly, that is why security has got to be enhanced at Sharm el-Sheikh."

She said EasyJet had suspended flights to Sharm el-Sheikh through the end of this month, as have all other British airlines.

"We will not resume flying until we are told unequivocally by the government that it is safe to operate at Sharm el-Sheikh airport," she said.