UK-based monitoring group the Syrian Observatory for Human Rights said it had recorded no civilian deaths in the first 15 hours of the truce.
Residents in the embattled northern city of Aleppo reported calm.
Separately, Israel denied on Monday that Syria had shot down one of its jets over the Syrian Golan Heights.
Syrian state TV reported the country's military had downed an Israeli warplane and drone after the aircraft attacked a Syrian army position in the Quneitra region.
The Israeli military said in a statement that it had attacked Syrian positions after a mortar bomb struck the Israeli-controlled area of the Golan Heights, but that two Syrian surface-to-air missiles missed its aircraft.
'Sporadic attacks'
The truce in Syria was reportedly broken by sporadic attacks carried out by both government forces and rebels after the ceasefire had come into effect.The Syrian Observatory said they had seen reports of aerial bombardment of some villages in Hama province, and shelling near Damascus.
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A number of rebel factions have given a guarded welcome to the deal but expressed reservations about its implementation.