BEIRUT (AFP) - An Australian who travelled to Syria to join Kurds battling militants has been killed, a monitor said Wednesday, adding he was the first Westerner to die fighting alongside the Kurds.

"An Australian man was killed in an assault on Tuesday by the Islamic State against a position of the Kurdish People's Protection Units (YPG) near Tal Hamis in Hasakeh province," said Syrian Observatory for Human Rights director Rami Abdel Rahman.

The Observatory had reported the fighter's death on Tuesday, but was unable to confirm his nationality until Wednesday.

"Dozens of Westerners have joined the YPG's ranks. There are foreigners fighting on all sides of Syria's war," said Abdel Rahman.

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

"The YPG 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," he said.

Some of them had previous combat experience because they had served in the army.

In December, Australia revealed that 20 of its citizens who had travelled to Syria and Iraq to join Islamic State in Iraq and Syria (ISIS) had been killed.

Australia also accused the militants of using foreign fighters as "cannon fodder, suuicide bombers and "propaganda tools".

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

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

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