Air strikes on Syria's northwestern Idlib region stopped on Saturday after a Russian-backed ceasefire went into effect following four months of deadly bombardment, a war monitor said.
"There are no warplanes in the sky and air strikes have stopped," said Rami Abdul Rahman, the head of the UK-based Syrian Observatory for Human Rights.
Clashes between regime loyalists and insurgents on the edges of the anti-government bastion have also ceased after a unilateral ceasefire by Syrian regime forces went into effect at 6am, he said.
Artillery and rocket attacks continued however despite the deal. On Saturday, missiles hit Al Qaeda-linked militants in northwestern Syria, the Observatory said, hours into the ceasefire, killing 40.
The attack near Idlib city hit "positions" belonging to the Hurras Al Deen. It was not immediately clear who was behind the attack, or if the missiles where launched from war planes or positions on the ground, the monitor added.
Russia on Friday announced that the truce's aim was "to stabilise the situation" in Idlib, one of the last holdout of opposition to forces of Syrian President Bashar Al Assad.
It came after Russian-backed regime forces advanced in the rebel-held bastion, with monitors reporting air strikes that killed civilians including children.
Also on Friday, hundreds of Syrian protesters stormed the Turkish border on Friday, marching on the Bab Al Hawa border crossing in northern Syria to demand that Turkey either open the border or do more to end the attacks by government forces.
In Washington, Secretary of State Mike Pompeo voiced concern over the "horrific effects" on civilians from the air strikes by Mr Al Assad and his allies.
"He underscored the need for an immediate return to a ceasefire," the State Department said in a statement after Pompeo met the UN special envoy on Syria, Geir Pedersen.
After months of intense bombardment, regime forces launched a ground offensive against Idlib earlier this month.
Syria's war has killed more than 370,000 people and displaced millions since it started in 2011.
Russia launched a military intervention in support of Mr Al Assad in 2015, helping his forces to reclaim large parts of the country from opposition fighters and jihadists.
It is the latest Russian-led effort to avert what the United Nations has described as one of the worst humanitarian "nightmares" in Syria's eight-year conflict
The Idlib region is home to some three million people.
Most of Idlib province and parts of neighbouring Aleppo and Latakia provinces are controlled by Hayat Tahrir Al Sham, a jihadist group led by Syria's former Al Qaeda affiliate.
Russia-backed regime forces have been pressing an offensive against the region despite a deal with rebel backer Turkey in September last year to protect the area.
Stepped up bombardment by Damascus and Moscow since the end of April has displaced 400,000, the UN says, and killed more than 950 civilians, according to the Observatory.
Earlier this month, Damascus scrapped a similar agreement only three days after it went into effect, accusing rebels and mnilitants of targeting a Russian airbase.
Mr Al Assad, who now controls around 60 per cent of the country, has vowed to reclaim the rest, including Idlib.
The Syrian conflict has killed more than 370,000 people and driven millions from their homes since it started with the brutal repression of anti-government protests in 2011.
Turkish President Recep Tayyip Erdogan said this week that Turkey would mount a cross-border offensive on its own to clear Kurdish militia from its border if necessary.