There has been fresh violence in several Syrian cities, opposition activists say, just hours before the Syrian government was due to announce a final decision on an Eid al-Adha ceasefire proposed by Lakhdar Brahimi, the UN and Arab League envoy.
The Syrian army fired heavy tank and rocket barrages on Thursday at the Damascus suburb of Harasta, activists said, after rebels overran two army checkpoints on the edge of the town.
There were also reports of at least one explosion in the city of Hama, though further details were not immediately available.
There were also reports that rebels had seized Aleppo's Ashrafiyeh district, a key area in the heights of the city on a route between its central and northern parts. Residents told AFP about 200 rebels had moved in to the area for the first time.
One 28-year-old resident said the rebels, who arrived on vehicles mounted with heavy machineguns and bearing the markings of the Liwa al-Tawhid main rebel unit, made it clear they were settling in for Eid despite the promises of a ceasefire.
"Snipers have set up in the buildings and 50 armed men, dressed in black and wearing headbands with Islamic slogans, entered a school near me. I heard them tell the residents: 'We are here to spend Eid with you'," he told AFP.
"I am waiting for things to calm down before leaving," he said.
Syria has said its military command is still studying a proposal for the ceasefire. Brahimi said in Cairo on Wednesday that both the government and most rebel groups would observe the truce for the Muslim holiday, which starts on Thursday and lasts four days.
Within an hour, though, 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, US envoy to the UN, said that "many are duly skeptical about prospects for even a temporary ceasefire, given Assad's records of broken promises".
She said the US "strongly supports" Brahimi's call for a ceasefire, but 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 during the talks.
Brahimi did not specify the precise time period for a truce. Nor did the initiative include plans for international observers.
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.