A ceasefire went into effect across large parts of Syria at midnight (2200 GMT Friday) after major rebel factions, President Bashar al-Assad's government and the largest Kurdish militia agreed to adhere to a "cessation of hostilities."
Calm prevailed in most fronts shortly after the ceasefire went into effect, a monitoring group said.
"After midnight we did not register any shelling or battles in Hama, Homs, Latkia and some areas in Aleppo as well as Daraa," said the head of the Britain-based Syrian Observatory for Human Rights, Rami Abdel Rahman.
Russian warplanes also did not fly out of Hemeimeem military airport in the coastal province of Latkia after midnight, Abdel Rahman said.
An activist who goes by the name of Fadi, told dpa that before midnight there were heavy clashes and shelling in the area of Daraya at the oustkirts of Damascus, but after midnight "it became quiet and we did not register any violations yet."
The Syrian army said Daraya would be excluded from the ceasfire because there are al-Nusra Front fighters in the area, a charge the opposition groups is in the town rejected.
The deal was brokered by the United States and Russia and excludes Islamic State, al-Qaeda's affiliate al-Nusra Front and other UN-designated terrorist groups.
The opposition, which has expressed doubts about whether the government would "exploit" the deal to advance its positions, said 97 rebel groups signed up and they would abide by the deal for up to two weeks.
Al-Nusra's leader rejected the truce and called for new attacks against the government.
Russia, which began airstrikes in Syria in September to bolster its ally Syrian President Bashar al-Assad, intensified its strikes in the hours before the ceasefire went into effect, bombarding opposition areas across the country.
While even the US has admitted there are good reasons to be sceptical about the deal, there is hope that it can at least allow humanitarian aid to reach besieged areas.
If the deal, which is vague on key points such as monitoring mechanisms, somehow manages to hold, the United Nations says it will seek to capitalize on the lower levels of violence and relaunch peace talks on March 7.
UN Syria envoy Staffan de Mistura told the UN Security Council that if the cessation holds and the humanitarian access continues unabated, he intended to reconvene the intra-Syrian talks on March 7.
Less than an hour before the ceasefire went into effect, the Security Council passed a resolution welcoming the it and demanding that all parties to the agreement fulfill their commitments to halt fighting.
After completing a five-day Syria trip, International Committee of the Red Cross head Peter Maurer said Friday that it was "time for the warring parties to end this horrendous conflict and for the world powers who can influence the situation to act decisively."
Al-Nusra is a key obstacle because it fights alongside rebels on important front lines. The rebels are concerned they will be attacked by Russia or the Syrian army under the pretext of hitting terrorists.
Another major concern is the dynamic between rebels, the Kurdish People's Protection Units (YPG) and Turkey in northern Syria.
Turkey, a staunch opposition supporter, has been shelling the YPG, which it views in the context of its three-decade-long civil war with Kurdish rebels on its own territory.
The YPG, backed by US airstrikes, has been gaining ground across the north, largely as it seizes territory from Islamic State, helping Washington achieve a key policy goal of weakening the extremists.
However, the YPG has also taken advantage of Russian strikes against rebels to take territory near Aleppo.
According to the last UN estimate in August 2015, some 250,000 people have been killed in the conflict that started in March 2011, when mostly peaceful protesters demonstrated against al-Assad's rule.
The Syrian Observatory for Human Rights, a pro-opposition monitoring group based in Britain, said in February that the conflict has claimed the lives of nearly 270,000 people.
The Syrian Centre for Policy Research think tank said in a report in February that 470,000 people have died in the civil war.