US Secretary of State Rex Tillerson says Washington sees no future for President Bashar Assad in Syria's government, insisting "the reign of the Assad family is coming to an end".
Tillerson made the comments on Thursday after what he called a "fruitful" discussion with UN Syria envoy Staffan de Mistura.
De Mistura is expected to reconvene UN-mediated peace Syrian talks in the coming weeks in the wake of recent battlefield gains by Assad's Russian-backed forces.
"The United States wants a whole and unified Syria with no role for Bashar Assad in the government," Tillerson told reporters.
"The reign of the Assad family is coming to an end, and the only issue is how that should be brought about."
America's top diplomat said that an exit of Assad should be done through the Geneva process led by de Mistura, but that such a departure was not a "prerequisite" for that process to start.
Tillerson also sought to play down any idea that the Syrian government's advances might amount to a "triumph" for Iran, which has been a key backer of Assad.
"I see Iran as a hanger-on," Tillerson said. "Iran has not been successful; the Russian government has been more successful. We have had success. I don't think that Iran should be given credit for the defeat of ISIS in Syria.
