An Australian has reportedly been killed in northern Syria after joining Kurdish forces fighting the Islamic State militia.

The London-based Syrian Observatory for Human Rights said an Australian was killed on Tuesday when Islamic State fighters attacked Kurdish militia near Tal Hamis in Hasakah province.

Tal Hamis is in north-east Syria, wedged between the Iraqi and Turkish borders.

A senior Kurdish official says former Australian soldier, nurse and Northern Territory Labor figure Matthew Gardiner has been in Hasakah providing medical care for Kurdish fighters.

But after the Observatory's report, the official told the ABC Mr Gardiner was alive.

The Observatory provided what it said were several images of the dead man, who was clearly not Mr Gardiner.

It said the source of the photographs in Syria knew the dead man well and claimed he spoke openly about his Australian nationality.

The source also said other Australians were active in the area, but none of their information could be independently confirmed.

The Observatory's director, Rami Abdel Rahman, said dozens of Westerners had joined the Kurdish ranks.

"There are foreigners fighting on all sides of Syria's war," he said.

"They are volunteers, they don't get paid anything at all.

"The YPG [Kurdish People's Protection Units] isn't actively recruiting foreigners, but people from countries like Canada, the United States, Britain, Spain, Australia, Holland, Austria and France have travelled to Syria to join their ranks."

Kurds are fighting IS on multiple fronts, with backing from a US-led coalition that launched strikes on jihadist positions in August, and Syria in September.

Westerners have also travelled to Iraq to join Christian groups battling IS, such as Dwekh Nawsha, whose name in the Assyrian language means 'self-sacrifice'.

The group was formed after IS launched a major assault around the Mosul area of Iraq that displaced hundreds of thousands of Iraqis from their homes.

ABC/AFP