A Syrian truce has come into effect after five years of civil war.
The “cessation of hostilities” began at midnight on February 27 with early reports saying front lines were silent.
UN special envoy for Syria Staffan de Mistura said fighting had “calmed down” but one breach was being investigated.
In the run-up to the deadline, President Barack Obama warned the Syrian government and its ally Russia “the world will be watching”.
The truce involves government and rebel forces, but not ISIS or the al-Qaeda-linked Nusra Front.
More than 250,000 Syrians have been killed in Syria’s civil war and millions more have been forced from their homes.
A few hours after the deadline passed, a car bomb killed two people outside the government-held town of Salamiyeh, near Hama, Syrian state media reported. It is not clear who carried out the attack.
Staffan de Mistura has said that peace talks will resume on 7 March if the truce “largely holds”, adding that he had no doubt there would be “no shortage of attempts to undermine this process”.
Russia said it would continue to bomb militant targets. Russian jets were reported to have intensified attacks on Syrian rebel positions on February 26.
In the run-up to the truce, heavy attacks around Damascus and Aleppo were blamed on Russian airstrikes, but denied by Moscow.
The cessation was brokered by the US and Russia, and is backed by a UN resolution. Previous talks in Geneva collapsed in early February after making no progress.
One of the key aims of the cessation is to allow desperately needed aid to reach people trapped in besieged areas.
The UN resolution names about 30 areas in dire need of aid, including eastern and western rural Aleppo and the eastern city of Deir al-Zour, which is under siege by ISIS jihadists.
Almost 100 rebel factions have agreed to respect the truce, Syrian opposition umbrella group the High Negotiations Committee (HNC) said.
However, the HNC warned the Syrian government and its allies not to use the “proposed text to continue the hostile operations against the opposition factions under the excuse of fighting terrorism”.
President Vladimir Putin says the Russian forces are targeting ISIS, Nusra Front and other extremist groups designated as legitimate targets by the UN Security Council.
However, Russia is widely accused of also attacking more moderate rebel groups fighting President Bashar al-Assad, an ally of the Kremlin.