The talks in Astana involving armed Syrian rebel groups are part of efforts to try to end the country's civil war that has killed more than 300,000 people since it began in 2011.
Russia's plan involves setting up four so-called de-escalation zones in rebel-held territory in Idlib, parts of Homs province, an opposition enclave near Damascus and Syria's south.
Rebels and government soldiers would be stationed at checkpoints around the four zones, and foreign troops could also be used in observer roles.
Russian president Vladimir Putin says Syrian and Russian planes would end their bombing in the four districts if opposition groups stop their attacks there.
The plan would allow for aid deliveries and the return of refugees.
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United Nations Special Envoy for Syria Staffan de Mistura says he supports the agreement.
"The most important thing is that this initiative today is actually a step in the right direction, because it's pushing for a concrete de-escalation in addition to the ceasefire in four areas."
Syria's ambassador to the United Nations, Bashar Ja'Afari, has also spoken in favour of the plan.
"The Syrian Arab Republic supports the Russian initiative on the de-escalation zones and stresses its commitment to the cessation of hostilities agreement signed on December 30, 2016, including not shelling those areas."
Kazakhstan foreign minister Kairat Abdrakhmanov says the zones would help improve the de-escalation process ahead of a round of talks in Astana in mid-July.
"(We have) adopted the memorandum on the creation of de-escalation areas in the Syrian Arab Republic, which foresees the establishment of de-escalation areas with a view to putting an end to ongoing violence, improving the humanitarian situation, creating favourable conditions to advance the process for a political solution of the Syrian conflict and an effective fight against terrorism."
But as Russia, Turkey and Iran gathered to sign the pact, Syrian rebel delegates shouted in protest and walked out.
Syria's armed opposition says it cannot accept establishing the safe zones, saying they threaten the country's territorial integrity.
And Syrian opposition delegation member Osama Abu Zaid says the rebels do not recognise Iran as a peace guarantor.
"In the name of the Syrian people, one of whose members, Major Yasser Abdul Rahim, who has objected on Iran signing, is present, we refuse any role for Iran and militias affiliated with it. We refuse for (Iran) to play any role as guarantor, considering it is a nation with hostilities against the Syrian people."
