Syrian state media said on Thursday the ceasefire would depend on militants fulfilling a Russian-Turkish deal that tried last year to create an Idlib buffer zone.
"The agreement to a truce was conditional. .This did not happen.. We resume our military operations against terrorist organizations," said the army statement.
For three months, an army offensive backed by Russia has killed at least 400 civilians in northwest Syria and uprooted more than 440,000 people, the United Nations says.
Residents and rescuers say the three-month-old campaign has left dozens of villages and towns in ruins.
Russia and its Syrian army ally deny their jets indiscriminately hit civilian areas with cluster munitions and incendiary weapons, which residents in opposition areas say are meant to paralyze everyday life.
Since Damascus declared a ceasefire on Thursday night, its warplanes have not mounted air strikes, though the combatants are still shelling each other.