The family of Shamima Begum – who left the UK to join the Islamic State group in Syria – have written to the home secretary challenging his decision to revoke her UK citizenship.
In the letter to Sajid Javid, seen by the BBC, they say they “cannot simply abandon her” and her status is “a matter for our British courts”.
But they added they are “sickened by the comments she has made” recently.
Ms Begum, 19, is living in a refugee camp in northern Syria.
She gave birth to a baby boy a few days ago.
The Home Office had said it was possible to strip the teenager of British nationality as she was eligible for citizenship of another country.