Syria's government and most opposition groups have agreed to a ceasefire during this weekend's Eid al-Adha holiday, the UN's peace envoy has said.
Lakhdar Brahimi said he hoped to use the lull in fighting to "discuss a longer and more effective ceasefire".
However, Syria's foreign ministry said the truce had not been agreed, and it would announce a decision on Thursday.
Rebels were split over the ceasefire plan, with one jihadist group saying it would not observe it.
The al-Nusra Front, a shadowy group that says it has carried out several high-profile bomb attacks, said it would not be tricked into playing "filthy games".
The main armed rebel group, the Free Syrian Army (FSA), said any ceasefire observed by the government would be reciprocated.
But the group's Gen Mustafa al-Sheikh added: "It is impossible that the regime will implement the truce, even if it says it will."
Eid al-Adha, the Festival of the Sacrifice, commemorates the willingness of Abraham to sacrifice his son Ishmael as proof of obedience to God.
In other developments:
- Syrian state TV says a car bomb has exploded in Damascus, killing six people and injuring 20 others
- BBC reporters in Damascus say warplanes have been flying over the capital and firing on some areas
- Opposition forces and the government blame each other for the killing of at least 16 civilians in Douma, a north-western suburb of the capital
Mr Brahimi has travelled across the Middle East over the past two weeks to promote his plan to use a ceasefire to kickstart a political process.
"There is agreement from the Syrian government for a ceasefire during the Eid," he told reporters in the Egyptian capital, Cairo.
"Other factions in Syria that we were able to contact - heads of fighting groups - most of them also agree on the principle of the ceasefire."
Mr Brahimi later briefed the UN Security Council, and they announced that they supported his plan.
Shortly after his announcement, the Syrian foreign ministry said the government was still studying the proposal and would announce its "final position" on Thursday.
But Russian diplomats said they had "indications" that Damascus would approve the plan.
Some analysts say divisions among the rebels over the ceasefire are just one part of the problem because there are also differences of opinion within the government.
While politicians might approve a ceasefire, the army and security officials are viewed by some as more likely to object and continue to push for a military solution.
The leader of the Syrian National Council, the main opposition coalition, told the Associated Press he had little hope the truce would take hold.
"This regime, we don't trust it, because it is saying something and doing something else on the ground," said Abdelbaset Sayda.
Earlier this week the UN's head of peacekeeping operations, Herve Ladsous, revealed he had started to make plans to send an observer force to Syria should a lasting ceasefire be agreed.
A ceasefire negotiated in April by Mr Brahimi's predecessor, Kofi Annan, broke down within days despite the presence of unarmed UN monitors.
The short-lived truce was followed by a dramatic escalation in the conflict.
Meanwhile, US Secretary of State Hillary Clinton warned that a power vacuum in neighbouring Lebanon could be exploited by Syria and create "even greater instability".
Lebanon's government was plunged into crisis after a senior security official was killed on Friday in a bomb attack that was blamed on Syria.