(BBC) A man who left London to join the Islamic State group in Syria has died while being held in prison in the country, the BBC has been told.
One source said that Ishak Mostefaoui, previously from east London, was killed while attempting to escape custody.
Another said the death came during serious disorder in a jail in Hassakeh, which houses IS prisoners from various countries.
The death and surrounding circumstances have not been officially confirmed.
After being captured last year, the 27-year-old was held in a prison in north-east Syria controlled by the Kurdish-led, US-backed Syrian Democratic Forces.
