The parents of a UK-Canadian man who joined the Islamic State group have said former Home Secretary Sajid Javid is a "coward" for revoking his British citizenship.
Jack Letts - dubbed Jihadi Jack - was 18 when he left his Oxfordshire school in 2014 to join IS fighters in Syria.
Sally Lane said her son had not been contacted ahead of the move, which his father likened to a "kick in the gut".
The Home Office said it would not comment on individual cases.
The Canadian government said it was "disappointed" the UK had "off-loaded" its responsibilities.
Mr Letts, who is a dual UK-Canadian national, was jailed after being captured by Kurdish YPG forces while trying to flee to Turkey in May 2017.
His parents, John Letts, 58, and Sally Lane, 57, were convicted in June this year of funding terrorism after sending their son £223.
They both told Channel 4 News they were "shocked" their son's citizenship had been revoked.
"It's kind of like you're [being] kicked in the gut," Mr Letts said.
He said it was a "really disappointing" move by the British government that was "just shirking responsibility and passing the buck off to the Canadians".
“It’s like you’re being kicked in the gut.”— Channel 4 News (@Channel4News) August 18, 2019
The parents of Jack Letts, often nicknamed 'Jihadi Jack’, give reaction to their son’s British citizenship being revoked for his membership of Isis in Syria. pic.twitter.com/ZRhbIcW2IX
The decision is thought to be one of the last made by Theresa May's government - when now-chancellor Sajid Javid was home secretary.
"I think it's maybe Sajid that's a bit of a coward and in denial and naive, and obviously it's his last act [as home secretary] and he can move on and not have to even justify it," Mr Letts's father said.
He added he would "love to have a debate" with Mr Javid about the decision.
Mrs Lane said it was a "real shock" the government did it without "any form of redress or discussion" with her son.
"He's being held incommunicado and has no access to a lawyer," she said.
Canada have also expressed disappointment in the government's decision.
A statement on behalf of Canada's public safety minister Ralph Goodale's office said: "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."
Canada added that it was aware some Canadian citizens were being detained in Syria, but there was "no legal obligation to facilitate their return".
"We will not expose our consular officials to undue risk in this dangerous part of the world."
Former defence minister Tobias Ellwood said removing the radicalised fighter's citizenship "shunts the responsibility elsewhere" when many fighters were "radicalised here in the UK".
He added that Britain "should be leading calls" on how "foreign fighters face justice and who is ultimately responsible for bringing them to justice".
DUAL NATIONAL FIGHTERS:— Tobias Ellwood MP (@Tobias_Ellwood) August 18, 2019
The character of conflict has changed but international laws have not been updated.
If are to stay safe and prevent ISIS 2.0 we must work with our allies and think more strategically than simply removing UK citizenship from radicalised dual nationals. pic.twitter.com/fLsWR1MTtQ
While the Home Office would not comment on the issue, a spokesman said: "Decisions on depriving a dual national of citizenship are based on substantial advice from officials, lawyers and the intelligence agencies and all available information.
"This power is one way we can counter the terrorist threat posed by some of the most dangerous individuals and keep our country safe."
Mr Letts, who converted to Islam when he was 16, dropped out of studying for his A-levels at a school in Oxford in 2014 before moving to Syria to join the so-called Islamic State.
The jihadist terror group became known worldwide for its brutal mass killings and beheadings.
In an interview with the BBC's Quentin Sommerville, Mr Letts said: "I know I was definitely an enemy of Britain."
After being pressed on why he left the UK to join the jihadist group, he said: "I thought I was leaving something behind and going to something better."
He told ITV News earlier this year that he wanted to return to the UK as he felt British - but understood it was unlikely he would be able to.
"I'm not going to say I'm innocent. I'm not innocent. I deserve what comes to me. But I just want it to be... appropriate... not just haphazard, freestyle punishment in Syria," he said, at the time. .
Following an Old Bailey trial, his parents were sentenced to 15 months' imprisonment, suspended for 12 months, for funding terrorism.
Under international law, a person can only be stripped of their citizenship by a government if it does not leave them stateless.
Mr Javid stripped Shamima Begum of her UK citizenship earlier this year.
She was one of three girls from east London who left the UK in February 2015 and travelled to Syria, where she married an Islamic State group fighter.
Mr Javid said Ms Begum could claim Bangladeshi citizenship because of her family background.
But Bangladesh has said she is not a citizen and would not be allowed into the country.