Interior Secretary Priti Patel said Islamic State bride Shamima Begum could never return to the UK.
Begum, who fled to join the terrorist group with two school friends in 2015, asked permission to return to Britain for therapy after the death of her three children in Syria.
But Patel said there was "no going back" and it was "pretty reassuring" to see the 19-year-old still in the war-torn country.
February 2019: Shamima Begum asks for “ mercy & # 39; & # 39; to politicians
"Our job is to keep our country safe," the interior secretary said on Sunday.
"We cannot allow people who harm us to come into our country – and that includes this woman.
"Whatever I see in terms of security and intelligence, I am simply not willing to allow anyone who is an active supporter or activist of SI in this country."
Patel added that he will "stop plasticizing" UK international obligations and "endanger the British public in the process."
Begum spoke to Sky News in February, days after the birth of the third baby
Begum of Bethnal Green, east of London, has been stripped of her British citizenship and currently lives in an internment camp in Syria.
Bangladeshi officials, where they are believed to be able to claim citizenship, said they could not enter the country.
Begum married Yago Riedijk, a Dutch IS wrestler, when he was 15 years old and had three children with him during his three years living with the terrorist group.
Begum married Dutchman Yago Riedijk in Syria
All three children died at an early age, with the last child born in February in a refugee camp.
Begum now claims to hate IS and said this week he was only there to "raise babies."