A bomb that brought down Russian Metrojet Flight 9268 in Egypt’s Sinai Peninsula last month was placed in the aircraft’s main cabin, the daily Kommersant said Wednesday, citing an unnamed source, according to Reuters. Earlier, it was reported that the bomb was placed in the aircraft’s cargo compartment.

The news comes just a day after Russian authorities confirmed that the jet was brought down by a bomb. The newspaper, which cited a person close to the plane crash investigation, said that the explosion’s epicenter was believed to be at the rear of the cabin, near the tails section. The Airbus A321 passenger plane was headed to St. Petersburg from Sharm el-Sheikh resort in Egypt when it crashed, killing all 224 people on board.

"According to a preliminary version, the bomb could have been laid under the passenger seat by the window. Its operation has led to the destruction of the frame and depressurization of the cabin, which had an explosive character," the newspaper reportedly said.

On Tuesday, Russian President Vladimir Putin vowed to hunt down those responsible for the plane’s downing. The Russian government also offered a bounty of $50 million for information on the perpetrators.

"After tests of the personal items and elements of the aircraft, examination has revealed traces of explosives on the [Airbus] A321," Alexander Bortnikov, head of the Federal Security Service of the Russian Federation (FSB), reportedly said Tuesday, adding that it was an "improvised, homemade bomb," with nearly 1.6 pounds of TNT.

Last week, British Foreign Secretary Philip Hammond said there was a “high probability” that a bomb placed by a supporter of the Islamic State group, also known as ISIS, had brought down the Russian jet. He reportedly added: “It may have been an individual who was inspired by ISIS, who was self-radicalized by looking at ISIS propaganda and was acting in the name of ISIS without necessarily being directed.”

On Tuesday, Russian airstrikes intensified in the Islamic State group’s stronghold in Syria.