An Australian man has reportedly been killed while fighting against Islamic State (IS) militants in Syria.

Social media accounts belonging to Kurdish military units claim 45-year-old former Australian Defence Force (ADF) soldier Jamie Bright died last week in the northern Raqqa countryside.

The ABC has so far been unable to independently verify Mr Bright's death, but the Australian man has appeared in recent online videos.

"The reason I came to Kurdistan is because of the people, their struggle and their fight," Mr Bright said in one of the videos.

"I came to help them in any way I can."

The ABC understands Mr Bright had been a member of the ADF, training with the School of Military Engineering in Sydney in the 1980s before being posted to Perth as an Army engineer.

The ABC also understands Mr Bright joined the YPG early last year and knew fellow Australian Ashley Johnston, who was killed by IS militants last year.

Mr Johnston, a former Army reservist originally from Queensland, was killed during an assault by Kurdish forces on an IS position near Tel Hamis, a tactically important area.

The Department of Foreign Affairs said it is unable to confirm his death, adding that Australians should not travel to Syria.