Britain has revoked the citizenship of a dual national Muslim convert to the Islamic State group dubbed "Jihadi Jack" being held in northern Syria, leading Canada to accuse the UK of off-loading its responsibilities.
The move targeting Jack Letts, 24, who was a dual UK-Canadian national, has prompted a diplomatic row with Ottawa, Britain's Mail on Sunday reported.
Former prime minister Theresa May approved the decision -- which had been made by then-interior minister Sajid Javid -- in one of her last actions before leaving office in early July, the newspaper said.
A spokesperson for Britain's interior ministry declined to confirm the report, noting it does not routinely comment on individual cases.
"Decisions on depriving a dual national of citizenship are based on substantial advice from officials, lawyers and the intelligence agencies and all available information," the spokesperson said.
"This power is one way we can counter the terrorist threat posed by some of the most dangerous individuals and keep our country safe."
However, the office of Canada's Public Safety Minister Ralph Goodale did confirm that "the United Kingdom revoked the citizenship of Jack Letts", and expressed disappointment at the move.
"Canada is disappointed that the United Kingdom has taken this unilateral action to off-load their responsibilities," the statement said.
"Terrorism knows no borders, so countries need to work together to keep each other safe".
Letts was captured by Kurdish forces in Syria and is languishing in jail there, despite saying in a media interview earlier this year he would like to return to Britain.
"I'm not innocent," he told ITV News. "I deserve what comes to me. But I just want it to be... appropriate... not just haphazard, freestyle punishment in Syria."
Letts converted to Islam at the age of 16 and fled his home in Oxfordshire, central England, two years later to join IS.
His Canadian father and British mother were convicted in a UK court in June of funding terrorism by sending him a small amount of money during his time in Syria, but were spared jail.
In an interview on British television Sunday evening, Letts' parents accused the British government of "shirking responsibility".
"It was a real shock that your government can do this to you without any form of redress or discussion or way of actually contacting Jack, given that he's being held incommunicado and has no access to a lawyer," his mother Sally Lane, 57, said.
"Jack and other people are now in a legal black hole," she said, adding that she has been told that the Canadian government has been trying to bring Jack back.
The Mail on Sunday also reported that there were concerns that the issue could overshadow a meeting between Canadian Prime Minister Justin Trudeau and Britain's new leader Boris Johnson at the G7 summit in France next weekend.
The decision is the latest instance of Britain revoking the citizenship of its nationals who went to join the Islamic State group's self-proclaimed caliphate.
In February it faced criticism after stripping Shamima Begum, a teenager who travelled to Syria to marry an IS fighter, of her British citizenship.