Jack Letts, Canadian father and British mother were convicted in a UK court in June

Britain has revoked the citizenship of a dual national Muslim convert to the Islamic State group dubbed "Jihadi Jack" being held in northern Syria, according to reports on Sunday.

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."

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 ISIS.

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.

The Mail on Sunday said revoking Letts citizenship had "sparked fury" in Ottawa, which believes he has little connection to the country.

The newspaper added there were fears the spat could overshadow a meeting between Canadian Prime Minister Justin Trudeau and British 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 traveled to Syria to marry an ISIS fighter, of her British citizenship.