A fragile ceasefire in Syria is hanging in the balance after fresh clashes between government forces and rebel fighters near the capital.
The truce, brokered by Russia and Turkey, was largely holding elsewhere in the country but by late Friday morning fighting had erupted in Wadi Barada in north-west Damascus.
It was not immediately clear which side started the fighting.
The Wadi Barada valley is a rebel-held pocket that the Syrian army and its allies have been trying to recapture in an offensive that started last week.
The regime had been bombing the area heavily until the truce came into force on Friday morning. A few hours of calm appeared to take hold after the midnight deadline, but by lunchtime the violence began again.
Millions of residents of Damascus and its suburbs have been without running water for a week following an attack on the Wadi Barada springs.
Rebels in the area said air strikes had damaged a water pumping station, while the government accused rebels of polluting the springs with petrol.
It was difficult to confirm the reports as the internet connection and phone lines in Wadi Barada appeared to have been cut. But one nearby resident said he could see four helicopters circling in the sky and heard heavy artillery fire.
The clashes were the most serious of several isolated incidents of violence. Several regime air strikes were also reported in western city of Hama and the northern opposition-held city Idlib.
Calm prevailed in most other areas included in the deal, however, and neither side wanted to declare it dead.
Opposition leaders expressed a cautious optimism that the truce - the third serious attempt at a nationwide ceasefire this year - would hold.
"We are more hopeful this time because Turkey is negotiating with Russia and not the United States, which was never able to achieve much", said a Free Syrian Army officer who did not give his name as he is not authorised to speak to the media. "But we cannot be surprised if this one fails too, as many have before it."
Russia and Turkey reached a detente earlier this year and have since managed to agree a truce in Aleppo as well as peace talks aimed at ending the seemingly intractable conflict.
And in a sign of growing cooperation between the opposing powers, Ankara and Moscow carried out their first joint raids against Islamic State of Iraq and the Levant (Isil), in the town of al-Bab near the Turkish border on Thursday.
Ankara launched an incursion into Syria more than four months ago to drive Isil away from its frontier. The jihadists are not included in the ceasefire.
The latest truce is the first reached without the involvement of the United Nations or US, reflecting the deterioration of relations between Moscow and Washington after the failure of previous diplomatic efforts on Syria..
While relations between Moscow and Washington appeared to worsen, Bashar al-Assad expressed hope that president-elect Donald Trump would be less hostile to his chief ally Moscow than his predecessor.
In an interview published on Friday, the Syrian president said that he believed the best chance for long-term peace in Syria was the mending of US-Russia ties.
"We can say part of the optimism could be related to better relations between the United States and Russia," Mr Assad said. "Good relations between these two superpowers will benefit almost the entire world, including small states like Syria. In this regard, we can say that a solution for Syria is possible."
Delegates from Mr Assad's government are expected to meet sometime in the new year with members of the opposition in the Kazakhstan capital Astana, where they will discuss a potential political settlement.
Sergei Lavrov, Russia's foreign minister, said the talks would be brokered by Ankara and Moscow but the US would only be invited to join after 20 January, when Mr Trump takes office.
The talks are the best hope of bringing to an end the nearly six-year-long war, which has cost the lives of nearly 500,000 people, displaced more than 11 million, and sparked the biggest migration crisis since the Second World War.
Ripples from the conflict have been felt all over the world, not least in deadly Isil terror attacks carried out against the West.
- Originally published in Telegraph UK