Updated

The U.N. envoy for Syria visited Russia on Thursday for talks focusing on future peace negotiations.

The envoy, Staffan de Mistura said his meeting with Russian Foreign Minister Sergey Lavrov comes at a "delicate, important moment" in Syria's six-year-old civil war.

He stressed the importance of coordination between U.N.-brokered peace talks in Geneva, which are aimed at resolving the conflict, and upcoming talks in Astana sponsored by Russia, Turkey and Iran, which are focused on reducing violence. De Mistura said the two tracks 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 the specifics of so-called de-escalation zones in Syria.

Russia, Iran and Turkey agreed to establish the zones, signing on to a Russian plan under which President Bashar Assad's air force would halt flights over designated areas across the war-torn country.

But fighting 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.

The next round of Astana talks, originally scheduled for June 12, has been pushed back to June 20, Lavrov's deputy Mikhail Bogdanov said.

"Intensive work is underway to clarify some details and prepare the relevant documents needed for the meeting in Astana," Bogdanov said in remarks carried by Russian news agencies.

Lavrov on Thursday emphasized the need to "harmonize 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."

De Mistura noted that the U.N. needs to "come up with new ideas all the time in order to keep the momentum in the direction of a political process."

He added that he will also meet Russian Defense 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 favor of Assad's forces.