Syrian and Russian warplanes mounted no air strikes in the rebel-held northwest on Friday after a ceasefire was announced.
Though rockets hit both Syrian government- and rebel-held territory on Friday morning, the Syrian Observatory for Human Rights said the level of violence was significantly reduced.
More than 400 civilians have been killed in the escalation over the past three months and more than 440,000 displaced, the U.N. Office for the Coordination of Humanitarian Affairs said last week.
Syrian state media reported that a ceasefire would apply from Thursday night on condition militants comply with an agreement between Russia and Turkey last year which aimed to create a demilitarised buffer zone.
There has been no official comment from rebels in the area, which is dominated by jihadist factions but where Turkey-backed opposition groups also operate. The Turkey-backed opposition is taking part in Syria talks being hosted by Kazakhstan.
Most of the opposition delegations at the talks had agreed to a ceasefire.