Russian President Vladimir Putin has announced a ceasefire between Syrian opposition groups and the Syrian government starting at midnight on Thursday.
The parties were also prepared to start peace talks, Mr Putin said, after Moscow, Iran and Turkey expressed readiness to broker a deal to settle the nearly six-year-old Syrian war.
The Syrian army announced a nationwide halt to fighting but said Islamic State and ex-Nusra Front militants and all groups linked to them would be excluded from the deal.
A spokesman for the Free Syrian Army, a loose alliance of rebel groups, said it would abide by the ceasefire and take part in future talks.
On Thursday Russia's embassy in Damascus was hit by a mortar shell, after being hit by shells twice on Wednesday. There were no casualties. The ministry said the attacks were a provocation aimed at derailing a peace settlement.
It's the third nationwide ceasefire agreed in Syria this year. The previous two, negotiated by Washington and Moscow, collapsed within weeks as warring sides accused each other of violations. The current deal does not involve the United States or United Nations.
The latest ceasefire deal follows a major defeat for the anti-Assad rebellion in Aleppo, where the Russian air force and Iranian-backed ground forces played a critical role helping the government drive rebels from eastern parts of the city.
It also follows a thaw in ties between Russia and Turkey.
One rebel commander expressed optimism that this deal would be more effective. "This time I have confidence in its seriousness. There is new international input," said Colonel Fares al-Bayoush, an FSA commander, without elaborating.
Talks on the latest truce picked up momentum after Russia, Iran and Turkey last week said they were ready to back a peace deal.
Mr Putin said opposition groups and the Syrian government had signed a number of documents, including the ceasefire, measures to monitor the truce, and a statement on readiness to start peace talks.
"The agreements reached are, of course, fragile, need a special attention and involvement... But after all, this is a notable result of our joint work, efforts by the defence and foreign ministries, our partners in the regions," Mr Putin said.
He also said Russia had agreed to reduce its military deployment in Syria.
Mr Putin spoke by phone to Mr Assad who said he was committed to observing the ceasefire, the Kremlin said.
Turkey said it and Russia would guarantee the ceasefire.
"This window of opportunity should not be wasted," Turkish President Tayyip Erdogan said.
The United States has been sidelined in recent negotiations and is not due to attend the next round of peace talks in Astana, capital of Kazakhstan, a key Russian ally.
However, Russian Foreign Minister Sergei Lavrov said the US could join the peace process once President-elect Donald Trump takes office next month.