Shamima Begum is not a Bangladeshi citizen and there is “no question” of her being allowed into the country, Bangladesh’s ministry of foreign affairs has said.
The UK has stripped the 19-year-old, who fled London to join Islamic State, of her British citizenship.
Such a move is only possible if an individual is eligible for citizenship elsewhere.
It was thought Ms Begum had Bangladeshi citizenship through her mother.
However, the ministry of foreign affairs said the government was “deeply concerned” she had been “erroneously identified” as a Bangladeshi national.
In a statement, it said Ms Begum had never applied for dual nationality with Bangladesh and had never visited the country.
It added that the country had a “zero tolerance” approach to terrorism and violent extremism.
Ms Begum was a schoolgirl when she left Bethnal Green in 2015, and was found in a Syrian refugee camp last week after reportedly leaving Baghuz – IS’s last stronghold.
She gave birth to a son at the weekend and now wants to return home.
Ms Begum’s mother is believed to be a Bangladeshi national, and lawyers have told the BBC that under Bangladesh law this means Ms Begum is automatically a citizen of the country as well.
But Ms Begum told the BBC’s Middle East correspondent Quentin Sommerville that she only had “one citizenship” and it was wrong for the UK to revoke it without speaking to her first.
“I wasn’t born in Bangladesh, I’ve never seen Bangladesh and I don’t even speak Bengali properly, so how can they claim I have Bangladeshi citizenship,” she said.
While he said he would not comment on individual cases, Home Secretary Sajid Javid has suggested Ms Begum’s baby could still be British.
He told the Commons: “Children should not suffer. So, if a parent does lose their British citizenship, it does not affect the rights of their child.”
Mr Javid said the power to deprive a person of citizenship was only used “in extreme circumstances”, for example, “when someone turns their back on the fundamental values and supports terror”.
But shadow home secretary Diane Abbott accused him of breaching the Universal Declaration of Human Rights, which states that “no-one shall be arbitrarily deprived of their nationality”.