A Canadian spy working as a double agent for Islamic State smuggled Shamima Begum and her two friends into Syria, according to a new book, The Secret History of the Five Eyes.
The book, according to The Times, claims that Britain conspired with Canada to cover up the role in the girls' disappearance.
Journalist Richard Kerbaj, the book's author, claims that Canada eventually admitted to the involvement of one of their agents because they feared the plot being exposed.
However, officials then successfully convinced their British counterparts to go along with the cover-up.
Reports suggest the Metropolitan Police was eventually told that the trio – all teenagers at the time – were trafficked to the terror group by a people smuggler informing for Canada’s intelligence agency.
But it has been alleged that the move was covered up, before Canada privately admitted being involved, but asked Britain not to publicly reveal what happened.
In recent years, Begum has been at the centre of a row over her rights after joining IS in 2015, the Metro recalls.
Having attempted to return to the UK four years later, she was stripped of her citizenship and told she would never be able to come back.
It has been alleged that Begum who is 23 now (then 15), and two other east London girls – Amira Abase, 15, Kadiza Sultana, 16 – were met by Mohammed Al Rasheed at Istanbul Train Station to help them get into Islamic State.
It is claimed that even as the Met launched an international search for the girls, Canada remained quiet – despite knowing what had happened to them.
Begum was found, nine months pregnant, in a Syrian refugee camp in February 2019.
The BBC also quoted a senior intelligence officer as confirming that Mr Rasheed was providing information to Canadian intelligence while smuggling people to IS.
In a forthcoming podcast for the BBC, called I’m Not A Monster, Ms Begum is quoted as saying: "He (Rasheed) organised the entire trip from Turkey to Syria… I don’t think anyone would have been able to make it to Syria without the help of smugglers."
"He had helped a lot of people come in… We were just doing everything he was telling us to do because he knew everything, we didn’t know anything," she said.
The revelations are likely to reignite debate around Begum’s citizenship, if it is confirmed that an intelligence officer working for a Western ally helped facilitate the infamous journey.
Begum initially said she did not regret her actions but has since apologised and claimed she was groomed.
She has denied any involvement in terror activities.
Sultana was reportedly killed in a Russian air raid, while Abase is missing.
Canadian and British intelligence have declined to comment.
According to the Metro, a spokesman for the UK Government said: "It is our longstanding policy that we do not comment on operational intelligence or security matters."
Begum said she married Dutch convert Yago Riedijk 10 days after arriving in IS territory.
She previously told The Times that she left Raqqa in January 2017 with her husband but her children, a one-year-old girl and a three-month-old boy, had both died.
Her third child died in the al-Roj camp in March 2019, shortly after he was born, the report noted.