An Australian man has reportedly joined a Christian militia fighting against the Islamic State terrorist group in northern Iraq.

Khamis Gewargis Khamis is stationed in a town called Baqofa, around 30 kilometres from the major IS-held city of Mosul, an ABC report said. Khamis, who is married with two children, joined an independent Assyrian militia known as Dwekh Nawsha, meaning "self sacrifices".

The militia was formed in response to IS' assault on the Assyrian minority in Iraq.

Khamis said that he was aware he might be breaking Australian foreign fighters laws by taking up arms with the militia, but that he was ready to defend himself if there were any consequences.