London (AFP) - A former Royal Marine has become the first Briton to be killed while fighting with Kurdish forces battling Islamic State jihadists in Syria, leaving his family "devastated" Wednesday.

Konstandinos Erik Scurfield, 25, died on Monday in a battle with IS militants, a source in the Kurdish People's Protection Units (YPG) told AFP.

"We are devastated to confirm the death of our son Konstandinos Erik Scurfield in Syria where he went to support the forces opposing Islamic State," his family said in a statement through the Foreign Office.

A YPG source said he had arrived in Syria on December 7 and joined the Kurdish militia.

Known as Kemal among fellow fighters, Scurfield died on Monday in a battle with IS militants south of Tal Brak town in Syria's northeastern Hasakeh province, the source said.

"We are in contact with the family to know what they want us to do with his body," the source told AFP by telephone.

He is believed to be the second Westerner to have died fighting with Kurdish forces against IS, after an Australian was reported killed in the same area last week.

- 'They need our help' -

Two British former soldiers returned home last year after a stint fighting IS while a 19-year-old serving British soldier was returned to his unit last month after fighting with the Kurds while on leave because "these guys need our help".

Dozens of Westerners are thought to have joined the ranks of the YPG in Syria and other militia battling IS, including Assyrian Christian forces in Iraq.

However, their numbers are dwarfed by the thousands of foreign jihadists who have joined IS since it seized swathes of Iraq and Syria and declared an Islamic "caliphate" last year, believed to include more than 500 from Britain alone.

MP Dan Jarvis said he had been in contact with Scurfield's family in recent weeks as they were "very worried" for his safety.

"Their worst fears have been realised," he said.

"Erik was an experienced former Royal Marine who was horrified by the atrocities being carried out by IS," Jarvis added.

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"His family's understanding was that he travelled to Syria hoping to provide medical and humanitarian support as an expert in battlefield medicine."

Mark Campbell, a pro-Kurdish rights campaigner, said he had informed Scurfield's mother of the news, and she broke down in tears.

"I really just wanted to inform her, to give her a message from the YPG that they have said they would love to bury Konstandinos as one of their comrades in arms, as a hero, but equally they also want to be guided by the family and will respect the wishes of the family."