"We demand and agree to this," Mazloum Abdi, head of the Syrian Democratic Forces -- the moribund autonomous Kurdish region's de facto army -- told reporters.

German Defence Minister Annegret Kramp-Karrenbauer has said she would raise the plan with her counterparts at an ongoing NATO meeting in Brussels.

NATO Secretary General Jens Stoltenberg said the German proposal would need UN approval to be implemented and therefore "needs to be discussed more in detail before any decision can be made".

The withdrawal of US troops from northern Syria earlier this month was followed by a string of rapid changes on the ground, with a Turkish invasion and Russian and Syrian government forces also rushing to fill the vacuum.

Moscow and Ankara signed a deal requiring all Kurdish forces to pull back from the border to behind a line 30 kilometres inside Syria, meaning they lost control over a huge slice of the Kurdish heartland.

Abdi has thanked Russia for its new role as the guarantor of a buffer between his forces and those of the Kurds' archfoe Ankara, but added he had "reservations" because Kurdish people in the that zone would be left unprotected.

The German initiative was embraced by the United States but has so far struggled to gain traction, and few details are yet available.

Abdi said he had spoken to French President Emmanuel Macron but admitted that the plan was still embryonic and needed endorsement from Russia, the dominant foreign broker on the Syrian conflict.

"We have communicated with many European countries, including those who announced the initiative. Two days ago I had a phone call with President Macron and we spoke about this project," Abdi said.

"I think it is under development... It needs American and Russian support," he said.