The family of IS schoolgirl Shamima Begum have received a letter from the Home Office saying they intend to deprive her of her British citizenship.
The family’s lawyer Tasnime Akunjee said that they were “disappointed” with the decision.
In a statement posted on Twitter, he said: "Family are very disappointed with the Home Office's intention to have an order made depriving Shamima of her citizenship.
"We are considering all legal avenues to challenge this decision."
ITV News reported a letter from the Home Office that was received by Ms Begum's mother on Tuesday.
It said Home Secretary Sajid Javid had ordered the move and explained it had already been processed.
"Please find enclosed papers that relate to a decision taken by the Home Secretary, to deprive your daughter, Shamima Begum, of her British citizenship," the letter read.
"In light of the circumstances of your daughter, the notice of the Home Secretary's decision has been served of file today (19 February), and the order removing her British citizenship has subsequently been made."
The letter asked the mother to let her daughter know of the decision and to inform her she has a right to appeal.
'Others have done a lot worse'
In 2015, she and two school friends from Bethnal Green fled the UK before making their way to Syria and were married off to Islamic State fighters.
Harjap Bhangal, a UK immigration lawyer said it was “surprising” because of how rare it was to revoke someone’s citizenship.
He told talkRADIO's James Whale: “Others have done a lot worse and not been stripped of their citizenship and been allowed back in.
“This grooming is done online and this must have been a serious amount of grooming for her to leave her whole family.
“You don’t leave your family, especially in an Asian family. It must have been something very serious to go out knowing what was in front of her.”