A ceasefire by Syrian government forces will come into force on Saturday morning in the rebel-held province of Idlib, Russia has announced.
The unilateral agreement will begin at 06:00 (03:00 GMT), Russia's defence ministry said.
Syrian forces intensified their efforts to recapture Idlib in April.
The UN says hundreds of thousands have since fled and at least 500 civilians have been killed in the province, where an estimated three million live.
Previous attempts to halt the fighting there have all only had limited success.
The announcement comes one day after Mark Lowcock, the UN's emergency relief coordinator, called on the Security Council to take meaningful action to protect civilians in Idlib.
"Dozens of communities have emptied out" and "entire towns and villages have been razed to the ground", he said, since the last conditional ceasefire collapsed.
Monitoring groups said on Friday that between 7,000 and 9,000 civilians had fled from the town of Maarat al-Numan alone in recent days.
Amid the growing exodus, there were also reports of clashes at one part of the Syrian-Turkish border on Friday.
Idlib, in the north-west, is the last stronghold of the rebel and jihadist groups that have been trying to overthrow President Bashar al-Assad since civil war broke out in 2011.
The province has been controlled by a number of rival factions, rather than a single group, since it fell to the opposition four years ago.
What has Russia said?
Russia, which has been supporting Mr Assad militarily since 2015, said an agreement had been reached for a ceasefire to start on Saturday morning.
In an announcement on Friday afternoon, it said the "unilateral ceasefire" aimed to stabilise the situation in Idlib. Its statement also urged anti-government fighters to "abandon armed provocations" and "join the peace process".
The ceasefire will be in effect in the "Idlib de-escalation zone" agreed last year by Russia and Turkey, which back opposing sides in the civil war.
What is happening in Idlib?
Forces loyal to the government launched an aerial offensive aimed at re-taking the area late in April and ground forces have also been making advances in recent weeks.
They have retaken key strategic locations, such as the town of Khan Sheikhoun - which had been held by rebels for five years.
The UN has issued repeated warnings that the offensive is causing a humanitarian disaster - within a civil war that has already taken hundreds of thousands of lives and displaced millions.
"Three million people - two-thirds of them women and children - are counting on your support to make this violence stop," Mr Lowcock said on Thursday.
Shortly before the new ceasefire was announced by Russia, there were reports of afternoon clashes between Syrian protesters and Turkish border guards by the Bab al-Hawa crossing.
Tear gas and warning shots were fired as hundreds gathered to demand Turkish help to end the offensive, AFP news agency reports.
There were also reports pro-Syrian government forces had taken control of the town of Tamanaa, in addition to several other villages and swathes of farmland in the south-east of Idlib Province.
The war in Syria: Five questions answered
How did the war start?
The country descended into war after President Assad's government used deadly force to crackdown on pro-democracy protesters, who took to the streets in March 2011 demanding political freedom.
Who is fighting?
That's complicated: President Assad's regime is fighting rebel groups ranging from pro-democracy groups to jihadist extremists, while a number of foreign powers are providing support to various sides.
How many people have died?
It is not known exactly, as death tolls vary according to the source, but it is estimated to stand at more than 500,000 dead or missing.
How many refugees are there?
More than 5.6 million people have fled Syria since 2011, with another 6.6 million internally displaced, according to the UN.
What has happened to President Assad?
His position looked tenuous at one point during the eight-year conflict, but thanks to international allies like Russia and Iran, President Assad has won back control of most of Syria, and has set his sights on Idlib.