Syrian Democratic Forces (SDF) fighters gather during an offensive against Islamic State militants in northern Raqqa province, Syria February 8, 2017.
Syrian Democratic Forces (SDF) fighters gather during an offensive against Islamic State militants in northern Raqqa province, Syria February 8, 2017. Reuters / Rodi Said

The U.S.-backed Syrian Democratic Forces would coordinate with Syrian government troops to fend off any Turkish invasion of the north, the SDF commander told Reuters on Sunday, saying Damascus should use its air defence systems against Turkish planes.

Ankara has vowed a new offensive on swathes of northern Syria controlled by the SDF, a Kurdish-led alliance that is spearheaded by the Kurdish People's Protection Units (YPG).

The new threats have highlighted the complex web of ties in northern Syria: while Turkey considers the YPG a terrorist organisation, Syrian Kurdish forces are backed by Washington and have also coordinated with Syria's government and its ally Russia.

SDF head Mazloum Abdi said on Sunday that his forces were "open" to working with Syrian troops to fight off Turkey but said there was no need to send additional forces.

"The essential thing that the Syrian army could do to defend Syrian territory would be use air defence systems against Turkish planes," he said in an interview by telephone from an undisclosed location in northern Syria.

Syria sees Turkey as an occupying force in its north and the foreign ministry in Damascus said last month it would consider any new Turkish incursions as "war crimes and crimes against humanity".

Turkey has backed rebel groups in clashes against Syrian President Bashar al-Assad's forces and the SDF. It has used warplanes and increasingly drones to target territory held by the SDF, where Syrian Kurdish authorities have set up a governance system separate from Damascus.

Abdi said more military coordination with Damascus would not threaten that semi-autonomous rule.

"Our priority is defending Syrian territory, and no one should think about taking advantage of that situation to make gains on the ground," he said.

Turkish President Tayyip Erdogan has vowed to capture the SDF-held towns of Tal Rifaat and Manbij in Syria's northern Aleppo province, most of which is otherwise held by Syrian government troops.

Turkish-backed incursions in previous years have ousted the SDF from the northwestern enclave of Afrin and a series of border towns further east.

Abdi said a new offensive would displace around one million people and lead to "wider" zones of fighting, but would not say whether the SDF would respond with attacks in Turkish territory itself.

He warned it could also lead to a resurgence of Islamic State, which the SDF ousted from swathes of territory in northern and eastern Syria with U.S. air support.

SDF fighters guard camps and prisons where IS fighters and IS-affiliated families are detained and re-deploying those guards to fight Turkey could leave security gaps.

"We cannot fight on two fronts," Abdi said.

He said he hoped an upcoming meeting between the foreign ministers of Russia and Turkey could lead to de-escalation but said any negotiated settlement must include a halt to Turkish drone attacks in northern Syria.

"This would be one of our essential demands," he said.