Several rebel groups say they are withholding their approval of any agreement until they receive more details.
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 opposed previous 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, and Turkish media reports quoted Foreign Minister Mevlut Cavusoglu as saying that a lasting cease-fire and political solution in Syria are "close." But no details were announced, and 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 prejudge intra-opposition talks.
Previous attempts at enforcing a nationwide cease-fire in Syria have failed, but the recent warming of ties between Russia and Turkey, who provide crucial support to opposing sides of the civil war, may prove to be a game changer.
The foreign ministers of Turkey, Russia and Iran met in Moscow last week for talks on Syria that pointedly included no Syrians, indicating they prefer to pursue a grand bargain among great powers rather than a domestic settlement between the government and the opposition.
The Anadolu report quoted unnamed officials as saying a plan for a cease-fire "in all regions" would be presented to the warring parties. The cease-fire would exclude terrorist organizations, it said, without elaborating on which groups would be left out.
It said peace talks in Kazakhstan would proceed under Russia and Turkey's leadership if the cease-fire holds, with the two acting as "guarantors" of any deal.
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.
Mosayyeb Naimi, a Tehran-based political analyst, said it was unclear whether Turkey could corral Syria's fractured opposition.
"Turkey's ability to convince armed groups to accept the cease-fire is unknown, particularly because Turkey is involved in conflict with some of those groups," he said. Naimi added that although the Russians have made initial agreements with Ankara, they may be waiting for U.S. President-elect Donald Trump to take office to discuss the U.S. role in the cease-fire process.
A top Russian diplomat meanwhile said a draft U.N. 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. 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 U.N. Security Council."
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 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.
Fraser reported from Ankara, Turkey. Associated Press writer Vladimir Isachenkov in Moscow and Mahdi Fattahi in Tehran contributed to this report.
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