Begum, now 19, was one of a group of three British schoolgirls who left London for Syria in 2015.
The family of a teenager who fled the UK to marry a member of the so-called Islamic State (IS) in Syria is “disappointed” that the Home Office intends to remove her British citizenship, their lawyer said.
A statement from Shamima Begum’s family, shared on Twitter by their lawyer Mohammed Akunjee, said her family is “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,” the statement added.
Akunjee confirmed to Euronews the legitimacy of a letter from the Home Office to Begum's family, obtained by ITV.
"Please find enclosed papers that relate to a decision taken by the Home Secretary, to deprive your daughter, Shamima Begum, of her British citizenship," it read.
"In light of the circumstances of your daughter, the notice of the Home Secretary's decision has been served of file today (19th February), and the order removing her British citizenship has subsequently been made."
Begum, now 19, was one of a group of three British schoolgirls who left London for Syria in 2015 after telling her family that she was going on a day out.
Speaking to The Times this month from al-Hawl refugee camp in northern Syria, a heavily pregnant Begum said she wanted to return to the UK, as she was worried for the well-being of her unborn child.
Begum's lawyer announced on Sunday that she had given birth to a baby boy.
The Home Office told Euronews on Tuesday evening it could not comment on individual cases.
In a later statement, a Home Office spokesperson said the home secretary had "clearly stated that his priority is the safety and security of Britain and the people who live here."
“In order to protect this country, he has the power to deprive someone of their British citizenship where it would not render them stateless.
"We do not comment on individual cases, but any decisions to deprive individuals of their citizenship are based on all available evidence and not taken lightly," the spokesperson added.