The United States is prepared to work with Russia on establishing "no-fly zones" in Syria as part of a joint effort to stabilize the war-ravaged country, America's top diplomat said Wednesday, ahead of President Donald Trump's first face-to-face with Vladimir Putin.

In a wide-ranging statement, Secretary of State Rex Tillerson said Russia had a "special responsibility" to help create stability on the ground -- or risk hobbling the fight against the Islamic State group.

Citing their past cooperation on the creation of deconfliction zones in Syria, Tillerson made a strong case for both countries -- in spite of their "unresolved differences on a number of issues" -- to work together in Syria.

"The United States is prepared to explore the possibility of establishing with Russia joint mechanisms for ensuring stability, including no-fly zones, on the ground ceasefire observers, and coordinated delivery of humanitarian assistance," he said.

Tillerson issued his statement before joining Trump in Europe, where the US leader will meet Putin for the first time on Friday on the sidelines of a G20 summit in Hamburg, Germany. Syria will loom large in their discussions.

It also came as US-backed fighters inch forwards in Raqa's Old City, in what Washington sees as a "key milestone" in the campaign to defeat the Islamic State group in its de facto Syrian capital.

"ISIS has been badly wounded, and is could be on the brink of complete defeat in Syria if all parties focus on this objective," Tillerson said. "In order to complete the mission, the international community, and especially Russia, must remove obstacles to the defeat of ISIS."

"We call upon all parties, including the Syrian government and its allies, Syrian opposition forces, and Coalition forces carrying out the battle to defeat ISIS, to avoid conflict with one another and adhere to agreed geographical boundaries for military de-confliction and protocols for de-escalation."

Russia, Turkey and Iran -- without the US -- agreed in May to establish four "de-escalation" zones in Syria. These are supposed to include no fly areas, where no warplanes can fly so as to guarantee the safety of civilians on the ground.

But on Wednesday those countries said they had failed to agree on the details, such as the boundaries of the zones and who will police them.

Tillerson also said Moscow as a key backer of Syrian President Bashar al-Assad has the responsibility of preventing his regime from further use of chemical weapons.

The United States launched a cruise missile attack on a Syrian air base in April in response to what it said was a government chemical weapons attack on civilians.

Sourc: AFP