British-born teenager Shamima Begum was recently stripped of her citizenship for joining the IS.
And the 19-year-old gave birth last month in a refugee camp in northeast Syria
Syrian Democratic Forces (SDF) spokesman Mustefa Bali confirmed to AFP that the baby had since died, but declined to specify how or when it happened.
He had previously denied the baby had died in a Twitter post that has since been deleted.
Ms Begum travelled from east London to Syria in 2015 and said she had previously given birth to two other children.
They are said to have also died, apparently from illness and malnutrition.
Britain stripped Begum of her citizenship last month despite her wishes to return to the country, although the government hinted her newborn son could be treated differently.
More in English via SBS News.
