The State Department raised concerns about the prominent role of Iran which like Russia has supported the Syrian military in its crackdown on opposition groups and attacks on civilians. | Getty Images U.S. expresses wary support for Russia-led cease-fire push in Syria

The State Department on Thursday expressed cautious optimism toward a new plan put forward by Russia, Turkey and Iran to establish so-called "de-escalation zones" inside Syria to reduce the violence, raising concern about Tehran's role in the effort.

"We appreciate the efforts of Turkey and the Russian Federation to pursue this agreement and have encouraged the Syrian opposition to participate actively in the discussions despite the difficult conditions on the ground," spokeswoman Heather Nauert said in a statement.


She said officials "hope that this arrangement can contribute to a de-escalation of violence, end the suffering of the Syrian people, and set the stage for a political settlement of the conflict."

But Nauert also raised concerns about the prominent role of Iran — designated by the State Department as a state sponsor of terrorism — which, like Russia, has supported the Syrian military in its crackdown on opposition groups and attacks on civilians.

The United States was not a direct participant in the discussions, which took place in Astana, Turkey, but was represented at the conference by Acting Assistant Secretary of State Stuart Jones.

"We continue to have concerns about the Astana agreement, including the involvement of Iran as a so-called 'guarantor,'" Nauert's statement read. "Iran’s activities in Syria have only contributed to the violence, not stopped it, and Iran’s unquestioning support for the Assad regime has perpetuated the misery of ordinary Syrians."

The new agreement is already reportedly being dismissed by some rebel groups who have been fighting the regime of Bashar Assad since 2011, and Nauert urged them to play their part.

"The opposition must also live up to its commitments, with Turkey as the guarantor, to separate from designated terrorist groups," she said, "which continue to hijack the legitimate aspirations of the Syrian people for a representative and accountable government."

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But Assad's actions going forward are seen as key. "In light of the failures of past agreements, we have reason to be cautious. We expect the regime to stop all attacks on civilians and opposition forces, something they have never done," the statement read. "We expect Russia to ensure regime compliance."

Russia joined Iran on the side of the Assad regime in 2015, a year after the beginning of a U.S.-led air campaign against the Islamic State, which still controls a large part of eastern Syria and northwestern Iraq.

"We look forward to continuing our dialogue with the Russian Federation on efforts to that can responsibly end the Syria conflict," Nauert said.