Russian Foreign Minister Sergei Lavrov said on Monday that the formation of a zone controlled by US-backed fighters could lead to the partition of Syria. The US has confirmed it is helping Syrian Kurdish fighters set up a border force of 30,000 personnel.

The troops will patrol the borders of territory carved out of northern Syria by the Syrian Democratic Forces, which are mainly composed of Kurdish YPG fighters.

The move has angered Russia, which still has troops in Syria, as well as NATO-member Turkey, which considers the YPG a terrorist group.

Al Jazeera's Rory Challands reports.