A German woman fighting alongside Kurdish forces in Syria was killed over the weekend in clashes with the militant Islamic State group, Kurdish officials said.

The Kurdish forces, backed by U.S. air strikes and local rebel fighters, have been battling Islamic State in northern Syria after the al Qaeda offshoot captured large tracts of land along the border with Turkey.

The woman, Ivana Hoffmann, was killed in a village near the town of Tel Tamr in northeastern Syria, Kurdish official Nasir Haj Mansour said. She had joined female Kurdish fighting units, known as the YPJ, two to three months ago, he said.

Nawaf Khalil, a spokesman for the Kurdish PYD party in Europe, confirmed she had died over the weekend.

The British-based Syrian Observatory for Human Rights said she was the third foreigner fighting alongside Kurdish forces to be killed in Syria's four-year-old war.

Last week the Observatory, which tracks the conflict using a network of sources on the ground, reported that another European had been killed further east, days after an Australian man died.

The Observatory estimates that just over 100 Western fighters have joined the Kurds in Syria and include Americans, French, Spanish and Dutch fighters, among other nationalities.

A Canadian-born immigrant to Israel was the first female foreign fighter to join the Kurds in Syria, a Kurdish source said last year.

The number of foreigners fighting alongside the Kurds is small in comparison with the thousands of foreign jihadist recruits to Islamic State and other hardline groups.