Aleppo was hit by air strikes and shelling on Wednesday, less than 24 hours after a ceasefire had been brokered to allow a withdrawal of fighters and civilians from rebel-held areas, dimming hopes that the long siege in Syria's largest city would end peacefully.
The resumption of bombing by government troops on an area packed with civilians "is almost certainly a violation of international law and most likely constitutes war crimes," said Zeid Ra'ad al-Hussein, United Nations High Commissioner for Human Rights.
"Dear world, there's intense bombing right now. Why are you silent? Why? Why? Why? Fear is killing me & my kids," wrote Fatemah al-Abed, whose Twitter account shared with her seven-year-old daughter, Bana, has become a symbol of the suffering in Aleppo.
Opponents of Syrian President Bashar al-Assad accused the government and its allies of scuttling the deal by adding new conditions, including the lifting of a rebel siege on two pro-government Shia villages in nearby Idlib province.
However, hours after it crumbled, the rebels said the deal was back on. There was no comment from the government or its allies, and minutes after the new ceasefire was to take effect late Wednesday, there were still reports of shelling in the few blocks of the city under rebel control.
Aleppo residents trapped in the besieged eastern sector reached by The Globe and Mail reported bombings that continued into the night.
"There was warplanes still attacking us here in the east and it was very shocking for us the things that are happening right now because we thought they were done with all the attacks," said Zouhir al-Shimale, exhausted after three nights of no sleep. Explosions could be heard in the background as he spoke.
Rami Zien, a Syrian activist, expressed frustration with the lack of international response to the crisis. "I think my message is that the people of Aleppo and people of other besieged areas in Syria generally will haunt you even in your dreams," he said.
The failed ceasefire had been brokered on Tuesday by Mr. al-Assad's Russian allies and Turkey, which supports some of the rebel groups fighting to topple the Assad regime.
Even if the truce had held, the latest developments effectively marked the end of the rebels' hold on Aleppo after more than three years of fighting, a significant victory for Mr. al-Assad, whose Shia-linked Alawite clan is backed by Iran and Russia.
In a bulletin, the Russian defence ministry accused the Jabhat Fateh al-Sham, formerly known as the al-Qaeda-linked Nusra Front, of breaching the ceasefire by firing rockets, tube artillery, mortars, grenade launchers and small arms.
Buses meant to pick up rebels and civilians at a crossing point outside east Aleppo left without passengers on Wednesday.
"The agreement was there, the buses were in place, the first convoy had set off and was then reportedly blocked by pro-government militia. This is inexcusable," the UN's Mr. al-Hussain said.
He added that, "The way this deal was dangled in front of this battered and beleaguered population – causing them to hope they might indeed live to see another day – and then snatched away just half a day later is also outrageously cruel."
Some 100 unaccompanied children are trapped in an east Aleppo building, according to UNICEF. "We remain extremely concerned about the well-being of these children. … Many have been separated from their families and have been surviving with the bare minimum for months," UNICEF spokeswoman Tamara Kummer said.
In an interview with the Russian-funded television channel RT livestreamed Wednesday, Mr. al-Assad spoke as if the battle of Aleppo was already over and accused Western countries of using the fighting there as a diversion to allow the militants of the Islamic State group to reoccupy the city of Palmyra.
He made no references to the collapse of the ceasefire in Aleppo but said he had agreed to a truce to limit civilian casualties "and to give a chance to those terrorists to change their minds."
However, the UN and Amnesty International have raised alarms about reports that advancing government troops have executed civilians and that hundreds of men who tried to cross into government-controlled areas have gone missing.
Reactions from Western officials underlined their frustrations and lack of leverage.
In an interview on France 2 television, French Foreign Affairs Minister Jean-Marc Ayrault said Wednesday that UN observers were needed to prevent a massacre.
During Tuesday's UN Security Council Emergency Briefing on Syria, U.S. ambassador Samantha Power singled out the Assad regime, Russia and Iran as being responsible for atrocities in Syria.
"We all know you are involved," she said. "Aleppo will join the ranks of those events in world history that define modern evil, that stain our conscience decades later. Halabja, Rwanda, Srebrenica and, now, Aleppo."
The Russian envoy, Vitaly Churkin, hit back, replying that Ms. Powers "gave her speech as if she was Mother Teresa herself. Please, remember which country you represent. Please, remember the track record of your country."
Turkish media reported that Turkey, Russia and Iran would hold a tripartite meeting on Aleppo on Dec. 27 in Moscow.
With report from Samya Kullab and Associated Press