"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.