Jets from the US-led coalition are barred from proposed safe zones in Syria set to be created under a deal inked by Russia, Iran and Turkey, Moscow's envoy said on Friday.

"In terms of their actions in the de-escalation zones then from this moment these zones are closed for their flights," the Kremlin's envoy to peace talks in Kazakhstan Alexander Lavrentiev was quoted as saying by Interfax news agency.

"Aviation operations, especially by the international coalition forces, are absolutely not envisioned," he said. Regime backers Russia and Iran and rebel supporter Turkey on Thursday signed a deal at talks in Kazakhstan to set up four safe zones in the war-torn country.

The agreement did not explicitly mention the US-led coalition, which has been targeting jihadists from the Daesh group, but Lavrentiev insisted that "flights cease over these territories."

"We as guarantors will closely monitor all operations," he said.

Moscow's envoy said this means coalition air power can now only focus on "Daesh targets that are located in the area of Raqa, some populated areas in the region of the Euphrates, Deir Ezzor and further on to the territory of Iraq."

The exact boundaries of the proposed safe zones in Syria are yet to be defined but they are meant to focus on rebel-held territory.

UN Secretary-General Antonio Guterres is encouraged by the safe zones agreement, his spokesman said. "It will be crucial to see this agreement actually improve the lives of Syrians," UN spokesman Stephane Dujarric said in a statement.

Guterres "welcomed the commitments to ceasing the use of all weapons, particularly aerial assets" and to quickly deliver medical aid and basic necessities, said the spokesman.

The United Nations will support de-escalation, said the spokesman but he did not elaborate.

UN envoy Staffan de Mistura, who was in Astana as an observer, described the agreement as "an important promising positive step in the right direction" toward a halt in the fighting. The United States however was extremely cautious, casting doubt over Iran's role even as it expressed hope that the deal could help set the stage for a settlement.

A working group will be set up within two weeks to resolve technical issues and the three countries agreed to set up the four areas by June 4.

The four areas include key territory held by anti-Assad forces.

The first zone includes the whole of Idlib province along with certain parts of neighboring Latakia, Aleppo and Hama provinces.

The second will encompass certain parts in the north of Homs province and the third will be comprised of some areas of Eastern Ghouta, outside of Damascus.

The fourth zone will include parts of the Deraa and Quneitra provinces in southern Syria, according to the memorandum seen by AFP.More than 320,000 people have been killed in Syria since the country's war began with anti-government protests in March 2011.

Working group to resolve technical issues

> A working group will be set up within two weeks to resolve technical issues
> The four areas include key territory held by anti-Assad forces
> The first zone includes the whole of Idlib province along with certain parts of Latakia, Aleppo and Hama provinces.
> The second will encompass certain parts in the north of Homs province
> The third will be comprised of some areas of Eastern Ghouta, outside of Damascus.
> The fourth zone will include parts of the Deraa and Quneitra provinces in southern Syria