Heavy clashes erupted between regime and rebel forces in Syria's divided city of Aleppo late Saturday after a unilateral ceasefire announced by regime ally Russia had expired.
Moscow had extended the unilateral "humanitarian pause" into a third day until 1600 GMT Saturday, but announced no further renewal of the truce despite a UN request for longer to evacuate wounded civilians.
"Members of popular civil committees from regime districts entered the eastern neighbourhoods to try to evacuate the injured but failed," Syrian Observatory for Human Rights head Rami Abdel Rahman said earlier Saturday.
The regime army opened eight corridors for evacuations, but just a handful of people crossed through a single passage, with the others remaining deserted.
More than 2,000 civilians have been wounded since the regime launched its offensive to drive the rebels out of the eastern districts they have held since 2012.
Nearly 500 people have been killed.
The United Nations had hoped to use the ceasefire to evacuate seriously wounded people, and possibly deliver aid.
But a UN official said Saturday the requisite security guarantees had not been received.
"You have various parties to the conflict and those with influence and they all have to be on the same page on this and they are not," said David Swanson, a spokesman for the UN humanitarian office.
Sporadic clashes between rebels and the Syrian regime and allied forces had been reported earlier on Saturday along frontlines, with some shells falling on both the regime-held western side of the city and the rebel-held east, the Observatory said.
Aleppo has been a major battleground in the Syrian conflict, now in its sixth year.
The regime's Bashar al-Assad, backed by the Russian military, Iran's Revolutionary Guards and an array of Shia militias, wants to take full control of the city.
Regime and Russian forces say they're targeting fighters linked to al-Qaeda from Jabhat Fateh al-Sham, formerly known as the Nusra Front, in eastern Aleppo.
Rebels say the regime and Russia are indiscriminately targeting civilians and civilian infrastructure to take over rebel-held eastern Aleppo.
Statue of Liberty made from bombed rubble of Aleppo, by Syrian artist Tammam Azzam. Devastating. pic.twitter.com/XTFpfSEtSR— ian bremmer (@ianbremmer) October 22, 2016