Syria has said its military command is still studying a proposal for an Eid al-Adha ceasefire with rebels, contradicting international mediator Lakhdar Brahimi's announcement that Damascus had agreed to a truce.
With the Muslim holiday beginning at sunset the day before, Thursday will be the first test of whether either side intends to silence their guns, at least temporarily.
Brahimi, the joint UN-Arab League special envoy, told a news conference in Cairo on Wednesday that both the government and most rebel groups would observe the truce for the Muslim holiday.
Within an hour, Syria's Foreign Ministry said in a statement that the proposal was still being studied and that "the final position on this issue will be announced (Thursday)".
A previous ceasefire arrangement in April collapsed within days, with the government and the opposition each accusing the other of breaking it.
Susan Rice, the American envoy to the United Nations, told reporters that "many are duly skeptical about prospects for even a temporary ceasefire, given Assad's records of broken promises".
She said the United States "strongly supports" Brahimi's call for a ceasefire, but she added that the "government must make the first move".
Brahimi has crisscrossed the Middle East over the past two weeks to push the warring factions and their international backers to agree to the truce - a mission that included talks with Syria's President Bashar al-Assad in Damascus at the weekend.
The Reuters news agency reported that Brahimi later on Wednesday told the UN Security Council that Assad had accepted a truce for the holiday, which starts on Thursday and lasts four days, during the talks.
Brahimi did not specify the precise time period for a truce. Nor did the initiative include plans for international observers.
The latest developments came as opposition activists and Syrian state media traded blame on Wednesday for the killing of at least 25 people, including women and children, in the town of Douma near Damascus.
"There was a horrible massacre in Douma last night," the media office of the opposition network in Douma said in a statement.
"More than 20 civilians have been slaughtered by shabiha [pro-government militia] who were at a checkpoint and then stormed into a residential building nearby."
In-depth coverage of escalating violence across Syria
Syrian state television said 25 people had been killed by "terrorist members of the so-called 'Liwa al-Islam.'"
State media labels opposition members as "terrorists".
In southern Damascus, state television said a car bomb in killed six people on Wednesday.
"The terrorist explosion caused by the car bomb in Daf al-Shok caused the martyrdom of six citizens and 20 wounded," a report said.
Meanwhile, Syrian warplanes carried out bombing raids on the strategic northern town of Maarat al-Numan and nearby villages while rebels surrounded an army base to its east, activists said.
Five people from one family, including a woman and child, were reported killed in the air strikes.
Maarat al-Numan has fallen to the rebels, effectively cutting the main north-south highway, a strategic route for Assad to move troops from the capital Damascus to Aleppo, Syria's largest city, where the rebels have taken a foothold.
But without control of the nearby Wadi al-Daif military base, the rebels' grip over the road is tenuous.
The rebels say the ferocity of counter-attacks by government forces shows how important holding the base is to Assad's military strategy.
As violence in the country continued, hundreds of refugees poured into a makeshift refugee camp at Atimah overlooking the Turkish border, fleeing a week of what they said were the most intense army bombardments since the uprising began.
"Some of the bombs were so big they sucked in the air and everything crashes down, even four-storey buildings," one refugee, a 20-year-old named Nabil, told Reuters at the camp.
"We used to have one or two rockets a day, now for the past 10 days it has become constant, we run from one shelter to another. They drop a few bombs and it's like a massacre."
The army relies on air power and heavy artillery to push back the rebels.
Human Rights Watch said the Syrian air force had increased its use of cluster bombs across the country in the past two weeks.
The New York-based organisation identified, through activist video footage of unexploded bomblets, three types of cluster bombs which had fallen on and around Maarat al-Numan.