The post-ISIL power vacuum in the region has brought tensions between Iran and Turkey to a head, analysts say.
The implementation of the agreement had a shaky start with fighting flaring in some areas.
The deal bans weapons in parts of Idlib, Latakia, Aleppo and Hama.
There is also hope for aid deliveries to about a million people living there.
The Syrian government has not signed the agreement but state media says leaders support the accord.
The main opposition groups have rejected the deal, saying it lacks “safeguards and compliance mechanisms”.
Turkey’s President Recep Tayyip Erdogan says “50 percent of the conflict” would be solved if the deal succeeds.
Does it represent a shift in diplomacy?
Presenter: Sami Zeidan
Hillary Mann Leverett, former White House national security official
Pavel Felgenhauer, Russian defence analyst
Molham Aldrobi, member of the General Secretariat of the Syrian National Council