A young German woman has been killed fighting alongside Kurdish forces against Islamic State group jihadists in northeast Syria.

Syrian Observatory for Human Rights head Rami Abdel Rahman says the woman in her 20s was "killed in the past few hours" in a battle for the Kurdish-held town of Tal Tamr in Hasakeh province.

The German, whose name was not immediately available, would be the third Westerner killed among Kurdish ranks in Syria.

Britain's Konstandinos Erik Scurfield and Australia's Ashley Johnston both died in clashes elsewhere in Hasakeh.

At least 40 Kurdish fighters and IS jihadists have been killed in the Tal Tamr battle, the Observatory said on Sunday.

News of the German woman's death, which was not immediately confirmed by Berlin, came on International Women's Day.

Women account for around 35 per cent of the fighting force of the Kurdish People's Protection Units, numbering around 7000, and they receive the same training as their male comrades.