Fighting subsided in Syria on Saturday after a deal signed by government backers Russia and Iran and rebel supporter Turkey to create four safe zones began to take effect, a monitor said.

The zones still exist only on paper and the cosponsors have until June 4 to finalise their borders under the terms of the agreement struck at peace talks in Kazakhstan on Thursday.

But the Syrian Observatory for Human Rights reported only sporadic skirmishes and shelling early on Saturday in the areas covered by the deal.

"Apart from a few exchanges and bombardments during the night and in the morning in Hama, Damascus and Aleppo provinces, violence was sharply reduced in the areas covered by the deal," Observatory chief Rami Abdel Rahman told AFP.

The agreement covers four main battlegrounds between the government and non-jihadist rebels -- the northwestern province of Idlib, parts of Homs province in the centre, the south, and the opposition enclave of Eastern Ghouta near Damascus.

It provides for a ceasefire, a no-fly zone, rapid deliveries of humanitarian aid to the designated areas and the return of refugees.

It builds on a ceasefire agreed between Russia and Turkey last December that reduced violence for a period but gradually fell apart.

The new proposal is significantly more ambitious, proposing the deployment of monitoring forces from the guarantor countries and seeking to ground all warplanes.

Some of its terms are ambiguous -- it does not specify that the safe zones take effect immediately but gives the three guarantor countries two weeks to form working groups to delineate them and then until June 4 to come up with the definitive boundaries.

It also calls for a continued fight against the Islamic State group and former Al-Qaeda affiliate Fateh al-Sham Front, which could pose challenges.

In Idlib province in particular, Fateh al-Sham is a major component of the rebel forces that control the area.

Washington has given the deal a guarded welcome. UN chief Antonio Guterres said he was "encouraged" by it.

More than 320,000 people have been killed in Syria since the country's war began with anti-government protests in March 2011. 

Source: AFP