The Kurdish-dominated Syrian Democratic Forces (SDF) has said it will support efforts to establish a safe zone in northeastern Syria.

The SDF, a coalition of armed groups backed by the US and led by the Kurdish YPG (People's Protection Units), said the zone must have "international guarantees…that would prevent foreign intervention", in an apparent reference to Turkey.

"We will offer all the support and assistance to set up the safe zone that is being discussed, in a way that guarantees the protection of all co-existing sects and ethnicities from annihilation," the group said in a statement on Wednesday.

It also said it hoped to ensure stability at the border region by reaching agreements with Turkey, which has vowed to crush the YPG.

The idea of a safe zone was suggested by US President Donald Trump on Twitter on Sunday, although he did not elaborate.

Turkish President Recep Tayyip Erdogan said on Tuesday he had discussed such a zone which Turkey would set up inside Syria along the length of their border, during a phone call with Trump.

Erdogan's comments came a day after he had a telephone conversation with Trump to ease tensions after the US leader threatened to "devastate" the Turkish economy if Ankara attacks Kurdish forces in Syria.

Earlier on Wednesday, a political leader of the Syrian Kurdish alliance Movement for a Democratic Society, said it would accept the deployment of United Nations forces along the separation line between Kurdish fighters and Turkish troops, in order to ward off a threatened offensive.

"Other choices are unacceptable as they infringe on the sovereignty of Syria and the sovereignty of our autonomous region," Aldar Khalil told AFP news agency.

Russia, meanwhile, said only its ally, the Syrian military, should police the war-torn country's north.

The YPG has been the key US ally in the fight against the Islamic State of Iraq and the Levant (ISIL, also known as ISIS), with an estimated 50,000 of its soldiers killed.

The anti-ISIL campaign is now nearing its conclusion with the group's fighters confined to an ever-shrinking enclave of just 15 square kilometres in Syria.

Ankara regards the YPG as an offshoot of the Kurdistan Workers' Party (PKK), which has waged a deadly war for autonomy in southeastern Turkey since 1984, and describes the armed group as "terrorists".

Syrian control

Russian Foreign Minister Sergey Lavrov said on Wednesday the Syrian government must take control of the country's north.

"We are convinced that the best and only solution is the transfer of these territories under the control of the Syrian government, and of Syrian security forces and administrative structures," Lavrov told reporters.

Russia is a long-time supporter of Syrian President Bashar al-Assad and Lavrov said the future of the Kurds could be secured under regime control.

"We welcome and support contacts that have now begun between Kurdish representatives and Syrian authorities so they can return to their lives under a single government without outside interference," Lavrov said.

He said there was progress in resolving Syria's nearly eight-year war that has killed hundreds of thousands of people, and the focus should remain on Idlib - the northwestern province that earlier this month fell under the full control of Hay'et Tahrir al-Sham, an armed group dominated by Syria's former al-Qaeda affiliate.

"The Syrian settlement is progressing, though of course more slowly than we would like," Lavrov said. "The fight against terrorism must be completed. Now the main hotbed of terrorism is Idlib."

Trump-Erdogan call

Erdogan said he had a "quite positive" telephone conversation with Trump late on Monday where he reaffirmed "a 20-mile [30-kilometre] security zone along the Syrian border [...] will be set up by us".

The Syrian Kurdish leader said he regretted the US proposal to give Turkey control over the security zone.

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"Sadly, Trump wants to implement these safe regions through cooperation with Turkey. But any role for Turkey will upset the balance and the region will not be safe," Khalil said.

"On the contrary, Turkey is a party [to the dispute] and any party cannot guarantee security."

Turkey has threatened to attack the YPG in the Syrian city of Manbij.

The Turkish army previously launched two major operations in Syria since 2016.

The last offensive saw Turkish troops and their Syrian rebel allies overrun the enclave of Afrin that was under the control of the YPG and its political arm, Democratic Union Party (PYD), in the northwest - one of several governed by the militia.