The UN Security Council has unanimously adopted a resolution supporting efforts by Russia and Turkey to end the nearly six-year conflict in Syria and jump-start peace negotiations.

The resolution approved on Saturday afternoon also calls for the "rapid, safe and unhindered" delivery of humanitarian aid throughout Syria. It also anticipates a meeting of the Syrian government and opposition representative in Kazakhstan's capital Astana in late January.

The final text dropped an endorsement of the Syria ceasefire agreement reached on Thursday, as Western members of the council sought changes to the circulated draft resolution to clarify the UN's role and the meaning of the agreement brokered by Moscow and Ankara.

Meanwhile on the ground in Syria, rebels warned that ceasefire violations by pro-government forces threatened to undermine a two-day-old agreement intended to pave the way for talks between the government and the opposition in the new year.

Vladimir Putin says Syrian ceasefire agreement has been reached with Turkey

Air strikes pounded opposition-held villages and towns in the strategically-important Barada Valley outside Damascus, activists said, prompting rebels to threaten to withdraw their compliance with a nationwide truce brokered by Russia and Turkey last week.

Rebels also accused the government of signing a different version of the agreement to the one they signed in the Turkish capital of Ankara, further complicating the latest diplomatic efforts to bring an end to six years of war.

Nearly 50,000 people died in the conflict in 2016, according to the Britain-based Syrian Observatory for Human Rights, which maintains networks of contacts on all sides of the war. More than 13,000 of them were civilians, according to the Observatory. Various estimates have put the war's overall toll at around 400,000 dead.

If the truce holds, 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. Those talks will be mediated by Russia, Turkey, and Iran.

Syrian foreign minister Walid Moallem and Major General Ali Mamlouk, head of the National Security Bureau, were in Tehran Saturday to discuss developments with their Iranian counterparts, according to Iranian state media. They met with foreign minister Mohammad Javad Zarif and Ali Shamkhani, secretary of Iran's Supreme National Security Council.

The Kremlin meanwhile said Russian President Vladimir Putin and Iranian President Hassan Rouhani confirmed their commitment to negotiations in Astana, in a phone conversation between the two leaders.

Iran and Russia have provided crucial military and diplomatic support to Syrian president Bashar al-Assad throughout the conflict, while Turkey has served as a rear base and source of supplies for the opposition.

The resolution also calls for "rapid, safe and unhindered" access to deliver humanitarian aid throughout the country.

The developments follow months of talks between Ankara and Moscow that culminated in a ceasefire agreement that went into effect on Friday at midnight.

But in a statement issued by a coalition of 11 rebel factions, including the powerful Jaysh al-Islam group operating in the Damascus countryside, rebels said they could not abide by the ceasefire if the government continued its assault on Barada Valley.

Aleppo before the Syrian Civil War Show all 12 1 /12 Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A man crosses a street in Aleppo, December 12, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A vendor sits inside an antique shop in al-Jdeideh neighbourhood, in the Old City of Aleppo, December 12, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A view shows part of Aleppo's historic citadel, overlooking Aleppo city, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A view shows part of Aleppo's historic citadel, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War Visitors walk inside Aleppo's Umayyad mosque, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War People walk inside the Khan al-Shounah market, in the Old City of Aleppo, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A man walks past shops in al-Jdeideh neighbourhood, in the Old City of Aleppo, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War People walk along an alley in al-Jdeideh neighbourhood, in the Old City of Aleppo, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War Visitors tour Aleppo's historic citadel, Syria December 11, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A general view shows the Old City of Aleppo as seen from Aleppo's historic citadel, Syria December 11, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War People walk near Aleppo's Bab al-Faraj Clock Tower, Syria October 6, 2010 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A man stands inside Aleppo's historic citadel, overlooking Aleppo city, Syria December 11, 2009 Reuters

The statement also complained that the government's version of the agreement signed in Ankara last week had deleted "a number of essential and non-negotiable points".

It said the opposition had agreed to a ceasefire encompassing the whole of Syria, without any exceptions to region or faction.

The Barada Valley Media Centre said Lebanese Hezbollah militants were firing on villages and towns in the water-rich region as Russian and government aircraft carried out raids for the 10th consecutive day on Saturday. The Lebanese militant group is a key ally to Mr Assad's forces.

The Barada Valley is the primary source of water for the capital and its surrounding region.

The government assault has coincided with a severe water shortage in Damascus since December 22.

Images from the valley's Media Centre indicate its Ain al-Fijeh spring and water processing facility have been destroyed in air strikes. The government says rebels spoiled the water source with diesel fuel, forcing it to cut supplies to the capital.

The Observatory reported at least two civilians and five militants have been killed in battles over opposition-held Eastern Ghouta and Barada Valley regions around Damascus, since the truce came into effect.

The Syrian military denied attacking the valley, saying it respected the Russian and Turkish brokered truce.

Meanwhile, Turkey's state-run Anadolu news agency reported the death of an Isis commander in a Turkish air strike near the north Syrian town of al-Bab on Friday. The truce does not cover operations against Isis or Jabhat Fateh al-Sham, the group formally known as Jabhat al-Nusra that claimed it split from Isis earlier this year.

Anadolu identified the commander as Abu Ansari. The report could not be independently verified.