A nationwide ceasefire in Syria brokered by the United States and Russia has gone into effect, the second attempt this year by Washington and Moscow to halt the five-year-old civil war.
The Syrian army announced the truce at 7 pm local time, saying a seven-day "regime of calm" would be applied across Syria. It reserved the right to respond with all forms of firepower to any violation by "armed groups".
Rebel groups fighting to topple President Bashar al-Assad issued a joint statement listing deep reservations with the agreement, which they say is unjust.
But while the statement did not explicitly back the ceasefire, rebel sources said the groups were abiding by it.
The agreement's initial aims include allowing humanitarian access and joint US-Russian targeting of jihadist groups, which are not covered by the agreement.
Russia's Foreign Ministry said in a statement that aid to the besieged city of Aleppo would start immediately.
Besher Hawi, a resident of the opposition-held city, said it had been calm since the ceasefire came into force, after a heavy day of bombardment.
"It's excellent but I certainly have no confidence in the regime. It could bomb at any moment," he told Reuters from Aleppo, speaking via a web-based messaging system.
Residents of government-held western Aleppo, frequently hit by rebel shelling, also expressed doubt over whether the truce would last.
"Every time there's a truce the militants... hit us," said an Aleppo resident who gave his name as Khaled. "We hope things will improve. May the army be victorious."
Hundreds of thousands of Syrians have been killed in the conflict and 11 million made homeless in the world's worst refugee crisis.
The ceasefire is the boldest expression yet of hope by the administration of US President Barack Obama that it can work with Russian President Vladimir Putin to end the war.
Hours before the truce took effect, an emboldened Assad vowed to take back all of Syria. In a gesture loaded with symbolism, state television showed him visiting Daraya, a Damascus suburb long held by rebels but recaptured last month after fighters surrendered in the face of a crushing siege.
"The Syrian state is determined to recover every area from the terrorists," Assad said in an interview broadcast by state media.