Mother-of-two Reema Iqbal, 30, and her sister Zara, 28, who has three young boys are believed to have been stripped of their UK citizenship.
Both sisters, from Canning Town in east London, whose parents are originally from Pakistan, are believed to have both married IS fighters who died in combat.
Both sisters left Newham in London in 2013 for the co-called Isil caliphate. At least one of their sons was born in the UK and was taken to Syria.
A Home Office spokesperson said: “Any decisions to deprive individuals of their citizenship are based on all available evidence and not taken lightly.”
The women’s parents are originally from Pakistan and it is possible the sisters would be eligible for Pakistani citizenship instead.
The sisters’ children, who are thought to be British citizens, would be unaffected by the Iqbal siblings losing their citizenship.
Reema Iqbal told a newspaper, she was hopeful of returning to the UK. She said: “The security services came to speak to me and I was honest, I told them my whole story so
Home secretary, Sajid Javid, was facing cross-party criticism after Kurdish officials confirmed that the three-week-old baby of Shamima Begum, 19, had died this week.
Mr Javid’s decision to remove Ms Begum’s citizenship prompted a fierce national debate over whether she should be allowed to return home, accusing him of breaking international law and condemning the decision as “callous and inhumane”.
Many politicians argued that it is illegal to leave a British citizen stateless.