The bomb which brought down a Russian jet that crashed after taking off from Sharm el-Sheikh killing 224 people was underneath the seat of a 15-year-old girl.

Maria Ivleva is thought to have been the first to perish in the tragedy when the jet blew up over the Sinai on October 31.

Crash investigators believe the explosive device was “likely” placed either under innocent passenger Maria’s seat, 31A, or that of 77-year-old Nadezhda Bashakova, who was sat behind her in 30A on the Airbus A321.

Maria was travelling back from holiday with her mother Marina Ivleva, 44, who was sat in seat 31B.

A report released today by Russian news organisation LifeNews said: “Investigators and secret service experts managed to locate the seat under which the terrorists planted the bomb which destroyed Airbus A321.

“The bomb which was equal to one kilo of TNT exploded and its forces went forwards and hit the rows up to 27. The wave went slightly backwards too and hit the row 32.

“The experts who tested the parts and bodies noted that the people who occupied the seats near the bomb, almost certainly died at once.”

One of the theories is that the bomb may have been stuffed into the compartment where a lifejacket is located.

ISIS has claimed responsibility for the bomb, and insist the device was contained in a Schweppes Gold can.

Moscow has offered a $50million (£33million) reward for information about the bomb.