Russia, Turkey, and Iran on May 4 signed a memorandum that calls for establishing safe zones in Syria where cease-fires are meant to be implemented -- including no-fly zones -- in order to ensure the delivery of humanitarian aid.
But Syria’s opposition delegation at the peace talks in Astana, Kazakhstan, where the memorandum was signed, has rejected the proposal.
Opposition delegates on May 4 accused Iran of being a party in the war and vowed that they will never support the safe-zone plan as long as Iran has any role as a cease-fire guarantor.
"Iran is a country that is killing the Syrian people and the killer cannot be the rescuer," said Abu Osama Golani, an opposition commander who attended the Astana gathering.
Osama Abud Zayd, a spokesman for Syrian opposition military factions, also expressed skepticism about Russia’s credibility in connection with the proposed safe zones, saying there is a "huge gap" between Russia’s promises and its actions.
Referring to a truce deal announced by Russia in December that has been largely ignored on the ground, Zayd said: "We have an agreement already in our hands...signed five months ago. Why hasn't it been implemented? Why are we jumping now to safe zones?
"Russia was not able to or does not want to implement the pledges it makes, and this is a fundamental problem," Zayd said.
Zayd also said Moscow had no answer to the question of how to deal with any violations of the cease-fire by Syrian President Bashar al-Assad's forces or by Iran, which has fighters on the ground supporting the government forces.
Iran and Russia have backed Assad's government throughout the war, while Turkey supports its some of Assad’s opponents.
As the memorandum was being signed on May 4 by Russia, Turkey, and Iran -- the three countries sponsoring the Astana talks and the three guarantors to the agreement -- part of the delegation representing Syria’s armed opposition shouted and walked out of the conference hall in protest.
"We do not accept Iran's involvement as a guarantor country," a member of the opposition delegation shouted while Kazakh Foreign Minister Kairat Abdrakhmanov was speaking.
The United States cautiously welcomed the Russia-backed plan for safe zones in Syria.
But in a May 4 statement, the State Department said it continues to have "concerns about the Astana agreement, including the involvement of Iran as a so-called "guarantor."
"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," it said.
It also said that while the Acting U.S. Assistant Secretary of State Stuart Jones attended the Astana conference, the United States was "not a direct participant in the negotiations and are not, at this point, a party to the agreement."
"In light of the failures of past agreements, we have reason to be cautious," the State Department said. "We expect the regime to stop all attacks on civilians and opposition forces, something they have never done. We expect Russia to ensure regime compliance."
Washington said Syria's opposition "must also live up to its commitments, with Turkey as the guarantor," to separate themselves from "designated terrorist groups," including the Al-Qaeda group Hay'at Tahrir al-Sham.
UN Special Envoy on Syria Staffan de Mistura called the agreement an "important, promising, positive step in the right direction in the process of de-escalation of the conflict."
He said the initiative "is actually a step in the right direction because it is pushing for a concrete de-escalation in addition to the cease-fire in four areas."
The memorandum calls for setting up four "de-escalation zones" in northern, central, and southern Syria, where Assad’s forces are fighting rebels in a war that has killed some 400,000 people since 2011.
The safe zones, originally proposed by Russia, would aim to end violence and allow for the return of refugees and the delivery of humanitarian aid.
They would be surrounded by checkpoints manned by opposition and government troops.
Foreign troops also could be deployed in observer roles.
The Turkish Foreign Ministry said the deal entails "nonconflict zones” in all of Idlib Province; parts of Lattakia, Aleppo, and Hama provinces; parts of Homs Province; and the Damascus suburb of Eastern Ghouta.
Ankara said the deal also would apply to areas of Daraa and Quneitra provinces.
Russian President Vladimir Putin’s special envoy for Syria, Aleksandr Lavrentyev, said the agreement will go into effect on May 6.
Lavrentyev said the armed opposition "would be directly combating terrorist organization groups" in the safe zones.
He said Russian warplanes would not fly over the designated zones and the Syrian Air Force was expected to refrain from flying over those areas, as well.
Lavrentyev said the Syrian government has vowed to abide by the agreement unless attacks are carried out against government forces by opposition groups in those areas.
He also said Turkey, Iran, and Russia have agreed on the possibility of allowing international observers to monitor the cease-fire if there is "unanimity" on that issue.
Lavrentyev said that if the cease-fire is "durable, then we could possibly talk about" the withdrawal of Iranian-controlled forces from Syria.
Abdrakhmanov said that the next round of talks in the so-called Astana process would be held in mid-July.
Russian President Vladimir Putin discussed the safe-zones plan with Turkish President Recep Tayyip Erdogan during a meeting on May 3 and with U.S. President Donald Trump by telephone on May 2.
The United States leads an international coalition that is conducting air strikes and other operations against Islamic State (IS) militants in Syria.
Russia says it is also battling IS in Syria, but Western officials say the Russian military operations have mainly targeted Assad's opponents.
The United States has mainly backed a separate UN-sponsored peace process in Geneva.