The military high command said in a statement "a regime of calm will be extended for a period of 72 hours from one o'clock on July 9".
The Syrian government uses the term "regime of calm" to denote a temporary ceasefire.
The previous 72-hour truce, which was accepted by the Free Syrian Army (FSA) rebel alliance but led to no noticeable decrease in violence, ran up to midnight on July 8.
That truce was the first to be declared across the whole country since one brokered by foreign powers in February to facilitate talks to end the five-year-old civil war. That truce has mostly unravelled, and the escalating violence caused talks to break down.