A British teenager who ran away to join Islamic State is set to lose her UK citizenship, the family’s lawyer has said.

Shamima Begum, 19, went to Syria to marry ISIS fighters in 2015 but wants to return to the UK with her baby boy.

“Family are very disappointed with the Home Office’s intention to have an order made depriving Shamima of her citizenship,” family lawyer Tasnime Akunjee tweeted.

“We are considering all legal avenues to challenge this decision.”

ITV News said Begum's mother had received a letter from the Home Office on Tuesday (local time) which said the Home Secretary had ordered the move.

"If you are in contact with your daughter, or are able to establish contact with her shortly, I would be very grateful if you could ensure the Home Secretary's decision is brought to her attention," the letter states, adding that Begum has the right of appeal.

Speaking to Britain's Sky News from Syria earlier this week , Begum said she didn't know what she was getting into when she left the UK at age 15.

"I think a lot of people should have sympathy towards me for everything I've been through," she said.

"I just was hoping that maybe for me, for the sake of me and my child, they let me come back, the young woman said. "Because I can't live in this camp forever. It's not really possible."

The teenager was one of a group of schoolgirls from London's Bethnal Green neighbourhood who went to Syria at a time when Islamic State’s online recruitment program lured many impressionable young people to its self-proclaimed caliphate.

Begum and her baby are reportedly in good health. (Supplied)

Begum said she had been only a "housewife" during her time with ISIS militants.

"I never did anything dangerous. I never made propaganda. I never encouraged people to come to Syria. So they'd only have proof I didn't anything that is dangerous," she said.

The teen added she had been "OK with" beheadings carried out by Islamic State adherents because she had heard it was allowed under Islamic law.