BEIRUT: Turkish and Russian officials are discussing the contours of a cease-fire for Syria, Syrian opposition factions said, building on cooperation between the two countries following a deal they brokered for the evacuation of opposition fighters from the northern city of Aleppo earlier this month.

Several rebel groups said, however, that they are withholding their approval of any agreement until they receive details about its terms.

An official with one of the factions told The Associated Press that Russian and Turkish officials were debating a cease-fire proposal that would encompass the whole of Syria. He spoke on condition of anonymity because the talks were ongoing. Rebels have spoken up in the past against proposals that would allow the government to continue its offensives around the outskirts of the capital, Damascus.

Turkey's Anadolu Agency said Wednesday morning that Ankara and Moscow had reached an agreement, but there was no confirmation from state officials.

The Syrian opposition official said factions were holding vigorous discussions over the possibilities.

Another official with a different group said the proposal has not been formally presented to the opposition.

"It is difficult to accept or refuse the matter before we look at the details, of course," said the official, who also spoke on the condition of anonymity so as not to bias intra-opposition talks.

The Anadolu report said a plan would be presented to all sides of the Syria conflict and aims for a cease-fire that would come into force "in all regions" where fighting between pro-government forces and opposition groups is taking place. It quoted unnamed officials.

Terror organisations would be kept out of the scope of the cease-fire agreement, the agency said, without elaborating on which insurgent groups would be considered terror organizations.

It said a peace process in Kazakhstan's capital of Astana would go ahead under Russia and Turkey's leadership if the cease-fire holds. Anadolu said the two countries would act as "guarantors" of the peace process.

Russian President Vladimir Putin's spokesman confirmed Russia and Turkey were in "constant contact" to prepare for planned Syria peace talks in Kazakhstan, but did not comment about the possibility of a cease-fire.

In the UN, a top Russian diplomat said a draft UN Security Council resolution that would impose sanctions on Syria for chemical weapons use is unacceptable to Moscow, which has veto power on the council.

A resolution drafted by Britain and France, which was obtained by The Associated Press, would impose sanctions on an array of Syrian individuals, organizations and companies allegedly involved in chemical weapons attacks in the war-torn country. It would also ban sales of helicopters to Syria.

Deputy Foreign Minister Sergei Ryabkov was quoted by the state news agency Tass on Wednesday as saying the resolution "is categorically unacceptable to us. We warn them against attempts to fan tensions in the UN Security Council."

And in Syria, activists said at least 20 civilians have been killed in an airstrike on an Islamic State-held village in Deir el-Zour province in eastern Syria.

The Britain-based Syrian Observatory for Human Rights monitoring group reported Wednesday that several unknown warplanes bombed the village of Hajna the night before, killing 12 people from one family and 10 from another. It said at least 10 children were killed.

The activist group Deir Ezzor 24 said no one in the two families survived.