The head of the Syrian Kurdish militia partnering with the U.S-led coalition to fight Islamic State militants says it is holding a "huge number" of foreign fighters in Syria and none of their home countries want them back.

Commander Sipan Hemo, speaking to reporters in a conference call Monday, says more than half of those detained in the battle against IS in Syria are foreign fighters from all over the world, including Russia, Europe, China, Japan and Arab countries. Many of the local fighters were forced to work with IS, he says.

Hemo gave no specific number but added it was a burden to keep them detained.

Hemo said, when asked, none of the countries wanted their detainees repatriated. "Honestly, we don't know what their future will be," He added.