A lawyer for the family of Shamima Begum, who was stripped of her citizenship after joining the Islamic State group, on Monday accused Britain of racism over her treatment, calling her a "tragic scapegoat".
Begum was just 15 when she and two other schoolgirls from east London travelled to Syria to join the jihadists, and was later tracked down in a refugee camp.
She had her citizenship revoked in 2019 on national security grounds, after an outcry led by right-wing newspapers.
But the UK's highest court last month ruled she could not return to Britain to appeal the decision.
Begum's family lawyer, Tasnime Akunjee, and the sculptor Anish Kapoor said she was "the tragic scapegoat of a punitive unforgiving government intent on harsh retribution".
"What happened to Christian forgiveness? Does it not apply to a woman -- and a dark-skinned one at that? It seems that different rules apply," they said in a joint statement.
"Is it perhaps that some of us are more British than others of us? Shamima is of Bangladeshi descent, does that change her right to British nationality?
"I am tempted to think it does especially in the light of the Supreme Court's judgment."
Kapoor, best known for his conceptual art installations, and Akunjee called the government's stance "a disgraceful indictment of our national conscience".
They suggested "four young white schoolgirls" from a less ethnically diverse area outside London would "no doubt" be treated differently.
"This is 'divide and rule', the horror that sustained the British Empire for 200 years. Have we regressed to now practising this on home turf?" they asked.
Begum married a Dutch IS fighter shortly after crossing into the militant group's territory from Turkey. She had three children, but they all died.
The Sunday Telegraph last weekend published pictures of Begum wearing Western clothing -- sunglasses, a T-shirt and a zip-up sweater -- at the Al Roj camp where she has been for the last two years.
She has previously been seen in a black niqab mandated by IS.
She agreed to being photographed, but she and others who came from Britain detained in the camp declined to be interviewed on the basis of legal advice, the weekly said.