A British woman who travelled to Syria as a schoolgirl to join the so-called Islamic State has lost the first round of her legal challenge against a decision to revoke her citizenship.

The Special Immigration Appeals Commission (SIAC) ruled that the government decision to strip 20-year-old Shamima Begum of her citizenship "did not make her stateless" as she was a citizen of Bangladesh by descent.

"The appellant (Begum) was in that situation as a result of her own choices, and of the actions of others, but not because of anything the Secretary of State had done," said judge Doron Blum referring to then-interior minister Sajid Javid.

The judgment was made despite SIAC finding that Begum could not have "a fair and effective appeal" against the decision as she is currently in a Syrian refugee camp.

Ms Begum's lawyer Daniel Furner said she would "immediately initiate an appeal" against the decision.

"The logic of the decision will appear baffling, accepting as it does the key underlying factual assessments of extreme danger and extreme unfairness and yet declining to provide any legal remedy," he said.

Ms Begum, then 15, was one of three schoolgirls from Bethnal Green in east London who left home to join the jihadist group on February 17, 2015. 

She claims she married a Dutch convert soon after arriving in IS-held territory. She was discovered, nine months pregnant, in a Syrian refugee camp in February last year.

Her newborn baby died soon after she gave birth. Two of her other children also died under IS rule.

Mr Javid removed her British citizenship soon after amid outcry. He has said more than 100 people had been deprived of their British citizenship.

Ms Begum took legal action against the Home Office last year.

Her lawyer, Tom Hickman, argued his client "is not considered a national of Bangladesh and was therefore rendered stateless" by the Home Office. 

The decision was unlawful as it breached the Home Office's extraterritorial human rights policy by exposing Ms Begum to "a real risk of death or inhuman or degrading treatment", he argued.

In the next stage of the process, the court will have to decide if the government had legitimate national security grounds to prevent her from returning to the UK.