A British teenager who ran away as a schoolgirl to join the Islamic State group has given birth to a baby boy in Syria.

Shamima Begum’s family lawyer said on Monday morning (Australian time) 19-year-old and her baby are in good health.

In a recent interview with The Times newspaper, Ms Begum said she had previously lost two babies to illness and malnutrition.

Ms Begum, who left Britain in 2015 at the age of 15 to become the bride of an IS fighter, is pleading to return back to the UK.

“People should have sympathy towards me for everything I’ve been through,” she told Britain’s Sky News from Syria, where she has been living in a refugee camp.

Asked if she had made a mistake by travelling to Syria, Ms Begum said: “In a way, yes, but I don’t regret it because it’s changed me as a person.”

“It’s made me stronger, tougher. I married my husband. I wouldn’t have found someone like him back in the UK.”

Under international law, the UK is obliged to let a Briton without the claim to another nationality back in.

Ms Begum was one of a group of schoolgirls from London’s East End who went to Syria to marry IS fighters in 2015, at a time when the group’s online recruitment program lured many impressionable young people to its self-proclaimed caliphate.

“I just was hoping that maybe for me, for the sake of me and my child, they let me come back,” Ms Begum said, adding that she had been only a “housewife” during her time with IS militants.

Shamima Begum has given birth, her family have been informed. Photo: AAP

“I never did anything dangerous. I never made propaganda. I never encouraged people to come to Syria. So they’d only have proof I didn’t … anything that is dangerous,” she said.

Ms Begum added she had been “OK with” beheadings carried out by IS adherents because she had heard it was allowed under Islamic law.

News about Ms Begum and her desire to go back to Britain has ignited a debate in the UK about how to deal with citizens who joined IS and want to leave Syria now that the extremist group is on the verge of collapse.

While it is unclear whether Ms Begum committed any crimes, many have focused on her apparent lack of remorse. In the earlier interview with The Times, Ms Begum said she did not regret her decision to join the extremists.

Her legal situation remains uncertain; she could face charges for supporting IS if she returns to Britain.

Two days before the baby’s birth was announced, Ms Begum’s relatives in Britain said they were “shocked” by her comments but thought she should be brought back and dealt with by the British justice system.

“The welfare of Shamima’s unborn baby is of paramount concern to our family, and we will do everything within our power to protect that baby, who is entirely blameless in these events,” the family had said.

The family said it is concerned about Ms Begum’s mental health and characterises her as having been groomed by IS fighters.

-with AAP