Major powers have agreed to a pause in combat in Syria, but Russia pressed on with its relentless bombing in support of its ally President Bashar al-Assad, who has vowed to fight on until he regains full control of the country.
Although billed as a potential breakthrough, the "cessation of hostilities" agreement does not take effect for a week, at a time when Assad's government is poised to win its biggest victory of the war with the backing of Russian air power.
If implemented, the deal hammered out at five hours of late night talks in Munich would allow humanitarian aid to reach besieged towns.
It was described by the countries that took part as a rare diplomatic success in a conflict that has fractured the Middle East, killed at least 250,000 people, made 11 million homeless and sent hundreds of thousands fleeing into Europe.
But several Western countries said there was no hope for progress without a halt to the Russian bombing, which has decisively turned the balance of power in favour of Assad.
Rebels said the town of Tal Rifaat in northern Aleppo province was the target of intensive bombing by Russian planes on Friday morning. The British-based Syrian Observatory for Human Rights, a monitoring body, said warplanes believed to be Russian also attacked towns in northern Homs.
Assad was quoted as saying he would continue to fight terrorism while talks took place. He would retake the entire country, although this could take a long time, he said.
Another week of fighting would give the Damascus government and its Russian, Lebanese and Iranian allies time to press on with the encirclement of Aleppo, Syria's biggest city before the war, which they are now on the verge of capturing.
They are also close to sealing the Turkish border, lifeline of rebel territory for years.
Those two victories would reverse years of insurgent gains, effectively ending the rebels' hopes of dislodging Assad through force, the cause they have fought for since 2011 with the encouragement of Arab states, Turkey and the West.
The cessation of hostilities agreement falls short of a formal ceasefire, since it was not signed by the main warring parties - the opposition and government forces.
Implementing it will now be the key, said US Secretary of State John Kerry: "What we need to see in the next few days are actions on the ground, in the field."
Russia suggested it might not stop its air strikes, even when the cessation of hostilities takes effect in a week's time.
Foreign Minister Sergei Lavrov said Moscow would not stop bombing fighters from Islamic State and a rebel group called the Nusra Front, which is affiliated with al-Qaeda, neither of which were covered by the cessation deal.
Britain and France said a peace deal could only be reached if Moscow stops bombing insurgents other than Islamic State.
US Defence Secretary Ash Carter said on Friday he expected Saudi Arabia and the United Arab Emirates to send commandos to help recapture Islamic State's eastern Syrian stronghold, Raqqa.
Assad said he believed Saudi Arabia and Turkey were planning to invade his country. Russia has said Saudi ground troops would make the war last forever.