A former Royal Marine has become the first Briton to be killed while fighting alongside Kurdish forces against Islamic State in Syria, a Kurdish militia has told the BBC.
The Kurdish Popular Protection Units (YPG) named him as Konstandinos Erik Scurfield, from Barnsley.
A British pro-Kurdish activist said he had informed Mr Scurfield's family of the death, at the request of the YPG.
The Foreign Office said it was "aware of reports" of a Briton dying in Syria.
The YPG said the "British volunteer martyr" died in an area west of the city of Qamishli on Monday.
A Kurdish commander said clashes against Islamic State (IS) in that area were continuing.
The BBC's Guney Yildiz said the YPG had asked Mr Scurfield's family if they could bury him in Syria "as a martyr".
In a statement, the Foreign Office said: "We are aware of reports of the death of a British national in Syria.
"The UK has advised for some time against all travel to Syria, where all UK consular services are suspended.
"As we do not have any representation in Syria it is extremely difficult to get any confirmation of deaths or injuries and our options for supporting British nationals there are extremely limited."
The BBC understands about 100 Western volunteers - including some Britons - are fighting as part of the 30,000-strong Kurdish forces.
More than 500 Britons are believed to have travelled to join IS.
BBC security correspondent Frank Gardner said the UK government's position was "probably going to lead to accusations of double standards".
He said if Britons went to Syria and were suspected of trying to join IS they would get their "collar felt at Heathrow" - but there "seems to be a silence about people going to fight on the other side".