BEIRUT, Feb 27 (Reuters) - A cessation of hostilities in Syria came into effect at the agreed time of midnight on Saturday (2200 GMT Friday), under a U.S.-Russian plan which warring sides in the five-year conflict have said they would commit to.
It was not immediately clear whether the various sides that signed up to the plan, including Damascus and its ally Russia, as well as a range of insurgent groups fighting against them, were respecting the halt in fighting.
The truce does not apply to Islamic State and al Qaeda affiliate the Nusra Front, and the Syrian government and Moscow have said they will not halt combat against those militants.
The United Nations unanimously demanded late on Friday that all parties to the conflict comply with the terms of the plan.
Fighting raged across much of western Syria ahead of the planned halt as heavy air strikes hit rebel-held areas near Damascus and insurgents battled government forces and their allies in Latakia province, President Bashar al-Assad's heartland.
Nusra Front on Friday called for an escalation in fighting, urging insurgents to intensify their attacks against Assad and his allies in a call that added to the dangers facing the fragile agreement.
Under the measure, which has not been signed by the Syrian warring parties themselves and is less binding than a formal ceasefire, the government and its enemies are expected to stop shooting so aid can reach civilians and peace talks begin.
Aid has been delivered to some besieged areas of the country this year in a series of localized agreements, but the United Nations demands unhindered access to all Syrians in need of help.
Peace talks collapsed earlier this month before they began, and Damascus and Moscow intensified assaults in the north and northwest of the country.
U.N. Syria envoy Staffan de Mistura said late on Friday he intends to reconvene peace talks on March 7 provided the halt in fighting largely holds.
The Syrian government has agreed to the cessation plan, but says it could fail if foreign states supply rebels with weapons or insurgents use the truce to rearm.
The main Saudi-backed opposition alliance, which has deep reservations, said it would accept it for two weeks but feared the government and its allies would use it to attack opposition factions under the pretext that they were terrorists.
The U.S.-backed Kurdish YPG militia, which is battling Islamic State in the northeast and Turkish-backed rebel groups in the northwest, said it would abide by the U.S.-Russian plan, but reserves the right to respond if attacked.