UN Secretary-General Antonio Guterres said he is encouraged by the agreement signed Thursday (May 4th) by Turkey, Russia and Iran to set up safe zones in Syria and de-escalate fighting, AFP reported Friday.

Russia, Iran and Turkey signed the agreement to set up the four safe zones following talks in the Kazakh capital Astana on shoring up a ceasefire agreed in December.

The agreement provides for a ceasefire, a ban on all flights, rapid deliveries of humanitarian aid to the designated areas and the return of refugees.

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

The UN will support de-escalation, he said, but did not make it clear what role it would play.

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".

But the US gave a cautious welcome, citing concerns over Iran's role as a guarantor, even as it expressed hope that the deal could facilitate 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 4th.

The first zone includes the whole of Idlib province, along with certain parts of neighbouring 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 Daraa and Quneitra provinces in southern Syria, according to the memorandum.