President Bashar al-Assad and his family have no role in the future Syria, U.S. Secretary of State Rex Tillerson said on Thursday ahead of peace talks aiming at a political transition scheduled to resume next month.

Tillerson said that the Trump administration backed the Geneva peace talks as the only way to end the more than six-year-old war and move to a political transition and elections.

He was speaking after holding talks with UN Special Envoy for Syria Staffan de Mistura, who announced that stalled peace talks between the Syrian government and still-to-be-united opposition would resume in Geneva on Nov. 28.

"The United States wants a whole and unified Syria with no role for Bashar al-Assad in the government," Tillerson told reporters in the Swiss city at the end of a week-long trip that took him to Saudi Arabia, Qatar, Pakistan and India.

"It is our view and I have said this many times as well that we do not believe that there is a future for the Assad regime and Assad family. The reign of the Assad family is coming to an end. The only issue is how that should be brought about."

Assad's father, Hafez, served as Syria's president for nearly three decades until his death in 2000.

When the Trump administration came into office it took the view that it was "not a prerequisite that Assad goes" before the transitional process started, he added.

Supported by Russian air power and Iran-backed militias, Assad appears militarily unassailable and last month Assad ally Hezbollah declared victory in the Syrian war.

Russian President Vladimir Putin, right, shakes hands with Syrian President Bashar al-Assad during a meeting at the Kremlin in October 2015. U.S. Secretary of State Rex Tillerson says Russia's air support was the predominant reason ISIS was turned back in Syria. (Alexei Druzhinin/RIA Novosti/Kremlin/Reuters)

Those forces have pushed Islamic State of Iraq and Syria (ISIS) back from large swathes of eastern Syria in recent months and over the past year have taken numerous pockets of rebel-held territory around Aleppo, Homs and Damascus.

Ceasefire deals brokered by Russia, Turkey, Iran and the United States in remaining rebel-held areas of western Syria have freed up manpower for Assad's allies.

Tillerson called his discussions with de Mistura "fruitful" and said the United States will "continue our efforts to de-escalate the violence in Syria."

He said the only reason Assad's forces had succeeded in turning the tide in the war against ISIS and other militants was "air support they have received from Russia."

Tillerson said Iran, Assad's other main ally, should not be seen as having made the difference in the defeat of Islamic State in Syria.

"I do not see Syria as a triumph for Iran. I see Iran as a hanger-on. I don't think that Iran should be given credit for the defeat of ISIS in Syria. Rather I think they have taken advantage of the situation."