The baby son of Shamima Begum - the teenager who fled London to join the Islamic State group - has died, a spokesman for the Syrian Democratic Forces has said.
A paramedic told the BBC the baby, who was about two weeks old, had a lung infection and died on Thursday.
Ms Begum, who left the UK in 2015, was found in a Syrian refugee camp in mid-February.
She wanted to return to Britain but was stripped of her citizenship.
The SDF - a US-backed, anti-IS rebel group that controls the camp where Ms Begum is living - confirmed the death on Friday. Its press officer had said earlier that the baby was alive.
Meanwhile, the paramedic, working for the Kurdish Red Crescent in and around the camp, said the baby had been suffering from breathing difficulties.
He was taken to a doctor on Thursday morning before being transferred to hospital, along with his mother, but died at 13:30 local time that day, the medical worker added.
The paramedic said both Ms Begum and her baby were taken back to the camp for burial.
'Nothing but sympathy'
Speaking to the BBC before it was confirmed whether the baby had died, Home Secretary Sajid Javid said: "Obviously I don't know whether that news is true or not but what I will say, sadly there are probably many children, obviously perfectly innocent, who have been born in this war zone."
He added: "I have nothing but sympathy for the children that have been dragged into this. This is a reminder of why it is so, so dangerous for anyone to be in this war zone."
Ms Begum, 19, gave birth to her son last month, shortly after being tracked down by a journalist in a Syrian refugee camp. She had reportedly left Baghuz - IS's last stronghold.
Ms Begum said she had previously lost two other children and named her newborn son Jarrah after her firstborn.
She said she wanted to return to the UK, but the Home Office stripped her of her British citizenship.
As her child was born before she was deprived of UK citizenship, the baby would still be considered British.
Earlier on Friday, the lawyer representing the family of Ms Begum, Tasnime Akunjee, said he had "strong but unconfirmed reports" that the baby had died.
We have strong but as yet unconfirmed reports that Shamima Begums son has died . He was a British Citizen.— Mohammed T Akunjee (@MohammedAkunjee) March 8, 2019
In an interview with the BBC after the birth of Jarrah, she said she did not regret travelling to Syria - although she added that she did not agree with everything the IS group had done.
She also said that she never sought to be an IS "poster girl" and simply wished to raise her child quietly in the UK.
Mr Javid previously said that the revocation of Ms Begum's citizenship would not apply to her son, saying: "Children should not suffer, so if a parent does lose their British citizenship it does not affect the rights of their child."
After Ms Begum was stripped of her citizenship, her family wrote to the home secretary to say they planned to challenge the decision and asked for assistance to bring her baby to the UK.
Earlier this week, Mr Akunjee tweeted a screenshot of the reply that they had received from the Home Office.
It told them that the possibility of bringing the baby to the UK was a matter for the Foreign and Commonwealth Office and that they would need permission from Ms Begum.
The FCO is obliged to consider requests for consular assistance, the letter added.
Ms Begum was a schoolgirl when she left Bethnal Green in east London in 2015. She married an IS fighter, a Dutch man called Yago Riedijk.