Guns fell silent across Syria on Saturday after a landmark UN-backed ceasefire came into effect.

Guns fell silent across Syria on Saturday after a landmark UN-backed ceasefire came into effect, as a special task force led by rivals Moscow and Washington prepared to begin monitoring the fledgling truce.

On the stroke of midnight, firing stopped in suburbs around the capital and the devastated northern city of Aleppo, AFP reported.

The nationwide cessation of hostilities is the first pause in five years of a civil war that has claimed more than 270,000 lives.

United Nations envoy Staffan de Mistura said peace talks would resume on March 7 if the agreement holds and more aid is delivered -- a key sticking point in negotiations for a truce.

Fighting appears to have "calmed down", he told reporters shortly after midnight, adding that a special task force would meet in Geneva on Saturday to monitor the ceasefire.

"The important point... is if (any) incidents will be quickly brought under control and contained," de Mistura said, adding that "a military response should be... the last resort".

Previous attempts to end the violence in Syria have failed and both Russia and the US have warned that stopping fighting on the ground will be difficult.

Less than an hour before the ceasefire began, the UN Security Council gave its unanimous backing to the truce in a resolution drafted by the US and Russia.

US Ambassador Samantha Power acknowledged there was "some skepticism" as to whether the ceasefire would last, but said it offered the "best chance to reduce the violence".

For his part, Russian Deputy Foreign Minister Gennady Gatilov said the agreement could be "a turning point" in the war.

But Russian President Vladimir Putin insisted Moscow would continue targeting Takfiri terrorist groups.

"The decisive fight against them will, without doubt, be continued," he said in televised remarks. "There is no other way."