A cease-fire deal between rebels and the Syrian government in the city of Aleppo has foundered, threatening plans to evacuate the remaining rebels and tens of thousands of civilians out of harm's way.
The withdrawal was supposed to start at dawn but shelling resumed in the morning hours and buses meant for the evacuations, which were waiting at the rendezvous point on the edge of the rebel enclave, returned to their depots.
Activists and rebels trapped in the opposition's last sliver of territory in Aleppo said pro-government forces had struck their district with dozens of rockets since mid-morning.
Syrian state television on Wednesday reported that rebel shelling of the Bustan al-Qasr district, recently recaptured by the army, had killed six people and injured others.
"The bombardment is scarcely to be believed on the eastern neighbourhoods and until now 40 people have been wounded," said Ibrahim al-Haj, a spokesman for the Syrian Civil Defense first responders. "They are using all forms of weapons."
The Syrian government ordered its green-coloured buses back, signalling that the deal mediated between Ankara and Moscow on Tuesday night to bring the fighting to an end in Aleppo was off.
The Lebanese al-Manar TV, broadcast footage of the buses leaving the evacuation point empty and said government forces had resumed fighting with rebels in the city.
Activists in eastern Aleppo blamed government forces, saying they shot first.
The Russian Defense Ministry said in a statement that the rebels "resumed the hostilities" at dawn, trying to break through Syrian government positions to the north-west.
Turkish Foreign Minister Mevlut Cavusoglu accused the Syrian government and its allies of trying to scuttle the deal.
The dramatic developments surrounding Aleppo - which would restore the remainder of what was once Syria's largest city to Mr Assad's forces after months of heavy fighting and a crippling siege - followed reports of mass killings by government forces closing in on the final few blocks still held by the rebels.