Two Syrian rebel groups in the town of Azaz have agreed a ceasefire.
The Islamic State in Iraq and Syria (Isis), linked to al-Qaeda, seized the northern town on Wednesday from the larger Western-backed Free Syrian Army.
The fighting between the two groups has raised fears of a possible war within a war.
The BBC’s Paul Wood, on the Syrian border with Turkey, says the two sides have agreed to exchange prisoners and hand back property.
It is unclear if the ceasefire will have an impact on clashes between the groups elsewhere in the country, he says.
Analysts say there is more chance that the US and other Western powers may arm the Free Syrian Army if it shows a distinct separation from the Islamists.
Meanwhile, Syria’s Deputy Prime Minister Qadri Jamil says the civil war has reached stalemate, with neither government forces nor the rebels strong enough to win.
He told the UK’s Guardian newspaper that at proposed peace talks in Geneva, Damascus would call for a ceasefire with the armed opposition.
Mr Jamil told the Guardian that the Syrian economy had suffered catastrophic losses in the civil war that began in early 2011.
More than 100,000 people have died in the conflict, according to the UN, and millions have fled the country or been made homeless.
No outright winner?
“Neither the armed opposition nor the regime is capable of defeating the other side,” he said. “This zero balance of forces will not change for a while.”
Mr Jamil – a former communist whose party took part in demonstrations against the government at the beginning of the uprising – insisted he was speaking for the government.
The BBC’s Jim Muir in neighbouring Lebanon says Mr Jamil’s comments are bound to be dismissed by the Syrian opposition, which is deeply sceptical about talk of reform and democracy from government sources.