A British man who joined the Islamic State group in Syria died while detained in the country, the BBC learned.
A source said that Ishak Mostefaoui, originally from east London, was killed while trying to escape from police custody.
Another said that the death occurred during serious unrest in a prison in Hassakeh, which houses IS prisoners from various countries.
The death and the surrounding circumstances have not been officially confirmed.
After being captured last year, the 27-year-old was detained in a prison in north-eastern Syria controlled by the Syrian Democratic Forces led by the Kurds and supported by the United States.
He is the first British ISIS supporter to die in SDF custody. Sources said he was one of 10 Britons and 30 Britons detained by the militia.
The prison where he was held is an old school. When the BBC spoke to him last October, he admitted to having joined IS.
- “At least seven from my university have joined IS”
The general situation in the prisons and camps where IS prisoners are held has deteriorated this year and there have been several riots.
The British government has refused to allow adult detainees to return to the UK, saying they should be tried in the area.
A government spokesperson told the BBC that the Foreign Office has advised against any travel to Syria since 2011.
They added: “Those who have chosen to leave the UK and fight for or support Daesh, potentially pose a very serious risk to national security.”
The SDF said foreign states should take responsibility for their citizens, saying earlier this year that IS prisoners were “a time bomb” and “we need to set up international courts, under the jurisdiction of the UN, and try them in the northeast of Syria where they committed their crimes. ”
Several countries have organized the return of certain citizens.
The ministers said that of the estimated 900 people who left the UK for Syria to join violent Islamist groups, 20% have died, 40% have returned to the UK and 40% are still in the region.
There are different accounts of the death of Mostefauoi.
The BBC received both versions: that he was killed while trying to escape, and the other that he was killed in recent riots.
ISIS propaganda channel on messaging application says he was killed while trying to get water during a prison siege which also prevented food and medicine from detained.
Last year, the BBC revealed that Mostefaoui was one of the many students at the University of Westminster to have traveled to Syria.
His Algerian family moved to London when Mostefaoui was five years old. He was described as a popular boy, a football lover, raised in a house opposed to extremism, but then became more and more radicalized as a student.
In April 2014, Mostfaoui told his father that he was going to Amsterdam for a few days, leaving with just a small bag, then he secretly went to Syria.
In 2018, Mostefaoui had his British nationality revoked.