BEIRUT (Reuters) - An Australian man who joined Syria Kurdish militants to fight against Islamic State jihadists has been killed, a group which tracks the conflict and a Kurdish source said on Wednesday.

The Syrian Observatory for Human Rights said the man died when Islamic State launched an assault on the Syrian Kurdish YPG militia, the group the man was fighting for in northeastern Syria.

Officials from the YPG refused to comment but a Kurdish source in northern Syria confirmed the news, asking not to be named.

Several foreigners, including Europeans and Americans, have joined the YPG in its fight against Islamic State. Their numbers are dwarfed by foreign jihadist recruits to the other side.

Kurds in Syria and Iraq are backed by a U.S.-led coalition which has been bombing Islamic State in both countries.