The young Jihadi bride who fled the UK to join Isis was "a member of the feared Isis morality police' in Syria", the Telegraph reported.
Shamima Begum, 19, who joined Isis as a 15-year-old, has always claimed she was "just a housewife" during her four years under the brutal Islamic State.
But now it has been alleged the teenager spent her days assisting suicide bombers by stitching them into suicide vests, carried a Kalashnikov rifle and enforced strict dress code as part of her role in the feared Isis morality police department.
The latest information about Begum was obtained by an allied spy agency and presented to British Prime Minister Theresa May and Home Secretary.
It is believed the information came from the CIA and Dutch Military Intelligence – during interrogation of other Western Isis converts.
A senior intelligence source told the Mail on Sunday: "She was involved and her former comrades have grassed her. She was literally stitching the vests, stitching them into the vests."
Begum's father Ahmed Ali has since broken his silence following the allegations, saying: "If she has done anything wrong, she should be brought to England and punished. As far as I know she was a housewife when in Syria."
The Begum family's lawyer, Tasnime Akunjee, has demanded to see any evidence held against the teenager, adding: "On behalf of the family, we would like to see this evidence, given that it has been leaked, and have it tested in proceedings in due course rather than through hearsay."
Following the collapse of Isis, Begum was found in a Syrian refugee camp by journalists where the 19-year-old told media she's never done anything dangerous, and begged to be allowed back in the UK.
"When I went to Syria, I was just a housewife. I just stayed at home and looked after my kids," she said.
"I didn't do anything dangerous. I never made propaganda, I never encouraged people to come to Syria. They don't have proof that I did anything dangerous."
Begum's UK citizenship was revoked, blocking her return to Britain, but a row sparked when her two-week-old son Jarrah died of pneumonia in a Syrian camp.
Jarrah was born a British citizen on February 16, shortly before Home Secretary Sajid Javid stripped his mother of her passport. Begum's British family had begged Javid to allow safe passage for Jarrah to come to London.