The move means that the repatriation of Letts will become the responsibility of Canada, rather than the UK.
London: Jack Letts, a British-Canadian national who converted to Islam and fled his home in Oxford to join the Islamic State (ISIS) five years ago, has been stripped of his British citizenship while being held in a Syrian prison.
The case of "Jihadi Jack" gained renewed attention in June this year after his parents --- John Letts, 58, and Sally Lane, 57 -- were convicted at London's Old Bailey on charges of terror financing, CNN reported.
But the move to revoke Letts' citizenship has sparked a diplomatic row between Britain and Canada as nations are not permitted under international law to deprive individuals of citizenship, especially regarding this case, whereby Letts, 24, had dual British-Canadian citizenship.
The move means that the repatriation of Letts will become the responsibility of Canada, rather than the United Kingdom.
"The government of Canada is aware that the United Kingdom revoked the citizenship of Jack Letts," Ralph Goodale, Canada's Public Safety Minister, said in a statement.
"Terrorism knows no borders, so countries need to work together to keep each other safe. Canada is disappointed that the United Kingdom has taken this unilateral action to off-load their responsibilities," the statement read.
"Investigating, arresting, charging and prosecuting any Canadian involved in terrorism or violent extremism is our primary objective. They must be held accountable for their actions," it added.
Letts was captured in 2017 by the People's Protection Unit, or YPG -- a US-backed Kurdish militia group combating ISIS -- as he attempted to flee into Turkey. The young man, nicknamed "Jihadi Jack" by the British media, has since been held in a jail in northern Syria.
Meanwhile, the UK's Home Office, which refuses to comment on individual cases, said that the decision to deprive dual nationals of citizenship is "based on substantial advice from officials, lawyers and the intelligence agencies."
"This power is one way we can counter the terrorist threat posed by some of the most dangerous individuals and keep our country safe," a spokesman told CNN in a statement.
Letts is believed to have converted to Islam at the age of 16. He subsequently began attending the Bengali mosque on Cowley Road, Oxford, and learned Arabic in order to study the Quran.
Speaking to the British press earlier this year from inside his jail, Letts admitted his guilt but expressed his desire to return to the UK.