Shamima Begum, who left the UK to join the Islamic State group in Syria aged 15, has a “right to return to Britain”, Labour leader Jeremy Corbyn has said.
Ms Begum has had her UK citizenship revoked by Home Secretary Sajid Javid – a move Mr Corbyn said was “extreme”.
Mr Corbyn told ITV News the 19-year-old should return to the UK in order to face questioning.
British nationals can only have their citizenship revoked if they are eligible for citizenship elsewhere.
It is thought Ms Begum could be a Bangladeshi citizen because she was born to a mother believed to be Bangladeshi.
However, Bangladesh’s ministry of foreign affairs has said Ms Begum is not a Bangladeshi citizen and there was “no question” of her being allowed into the country.
Mr Corbyn, who is currently in Brussels to discuss his Brexit proposals, said: “She obviously has, in my view, a right to return to Britain.
“On that return she must obviously face a lot of questions about everything she has done and at that point any action may or may not be taken.
“But I think the idea of stripping somebody of their citizenship when they were born in Britain is a very extreme manoeuvre indeed.
“Indeed, I questioned the right of the home secretary to have these powers when the original law was brought in by Theresa May when she was home secretary.”
Mr Javid has defended the move, which followed a debate over whether the teenager should be able to return to the UK after she was found in a Syrian refugee camp.
The home secretary said he would not leave an individual stateless – which is illegal under international law – but the Begum family’s lawyer, Tasnime Akunjee, said he was considering whether she has been left stateless as he prepares an appeal.
Ms Begum, who left east London in 2015, said she never sought to be an IS “poster girl” and now simply wished to raise her child quietly in the UK.