Speaking at the start of his meeting with Russian Foreign Minister Sergey Lavrov, Staffan de Mistura said it comes at a "delicate important moment" in Syria's 6-year civil war.
He stressed the importance of coordination between the talks in Geneva and the upcoming talks in Astana sponsored by Russia, Turkey and Iran, saying they are "closely interconnected."
"Without a good de-escalation process Geneva talks will be difficult, but without the Geneva progress there will be no horizon," he said.
The Astana talks set for later this month will focus on specifics of de-escalation zones in Syria.
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Violence had been reported in the "de-escalation zones" since the deal was struck, and details related to the zones and the monitoring process are yet to be worked out.
Lavrov emphasised the need to "harmonise the efforts taken by various players in Syria ... To protect Syria's sovereignty, uphold the rights of all ethnic and religious groups, ensure the security of the region and prevent Syria from becoming a constant source of terror threats."
He added that he will also meet Russian Defence Minister Sergei Shoigu for discussions "related to the humanitarian assistance, de-mining and linked to the consolidation of the de-escalation environment."
Russia has conducted an air campaign in Syria since September 2015, helping turn the tide in the conflict in favour of Assad's forces.