The United Nations Security Council on Saturday backed efforts by Russia and Turkey to push through with a truce in Syria and hold new rounds of peace talks next month, despite counter-accusations of violations by the Syrian government and rebels, and a fresh warning from some insurgents to abandon the deal amid complaints of bombardment on Wadi Baradi, a rebel-held strategic valley northwest of Damascus which supplies water for around four million people in the Syrian capital.

The resolution welcoming the ceasefire, the third truce this year seeking to end nearly six years of war, was adopted unanimously by the 15-member Council, meeting in New York. 

The deal brokered by Russia and Turkey, which back opposing sides in the Syria crisis, is considered as largely holding after coming into effect midnight on Friday, despite mutual claims of breaches.

The ceasefire is a prelude to peace talks that have been agreed on between Russia, Turkey and Iran. If the truce sticks, the government and the opposition will be expected to meet for talks for the first time in nearly a year in the Kazakh capital of Astana in the second half of January. Despite being mediated by the three countries, Russia’s ambassador to the UN Vitaly Churkin has said that other key players including the United States are welcome to participate. 

On Saturday, Russian President Vladimir Putin and his Iranian counterpart Hassan Rouhani agreed in a telephone call to work together to try to end the Syria crisis and make a success of peace talks planned for Astana, the Kremlin said in a statement. 

However, on the Syrian ground, firefights, air strikes and shelling went on in some areas, with insurgents warning to pull out if alleged violations continued.

Factions belonging to the Free Syrian Army – a loose alliance of militias excluding more radical Islamist groups – said government forces and Iranian-backed Lebanese Hezbollah fighters had been trying to push rebels back in the Wadi Barada valley.

 "Continued violations by the regime and bombardment and attempts to attack areas under the control of the revolutionary factions will make the agreement null and void," said a statement by the rebel groups. 

Meanwhile, a twin suicide bombing killed at least two people in the Syrian coastal city of Tartous in an area under government control and in President Bashar al-Assad's coastal heartland shortly after midnight on Sunday, state media and monitors reported.

(This story contains reporting elements from Reuters and The  Associated Press)