Shelling and air strikes sent terrified residents running through the streets of Aleppo on Wednesday as a deal to evacuate rebel districts of the city was in danger of falling apart.
The agreement reached Tuesday was meant to pave the way for thousands of civilians and rebel fighters to evacuate Syria's second city, scene of some of the worst fighting in more than five years of war.
But cold and hungry civilians who had gathered before dawn to evacuate were instead plunged back into a familiar nightmare.
"Bombing is ongoing, no one can move. Everyone is hiding and terrified," activist Mohammad al-Khatib told AFP from inside the city.
"The wounded and dead are lying in the street. No one dares to try and retrieve the bodies."
The evacuation, agreed under a deal brokered by Russia and Turkey, had been due to begin at 5:00 am (0300 GMT) but was delayed, with buses parked outside rebel-held areas left waiting.
Following several hours of quiet, fighting then erupted anew in the ravaged city, with Syria's regime, the rebels and their foreign allies trading accusations of blame.
As booms of air strikes and artillery fire rang out, an AFP correspondent in rebel areas saw panicked civilians running in the streets to find shelter, some hiding in the doorframes of damaged buildings.
The correspondent saw several wounded civilians, as well as a regime tank turning its cannon towards opposition-held districts and opening fire.
The Syrian Observatory for Human Rights reported "very intense clashes on every front line" and said at least two people had been killed in rebel areas.
State television said rebel rocket fire on government-controlled areas had also resumed, killing at least seven people.
Turkish President Recep Tayyip Erdogan said he would speak with Russian counterpart Vladimir Putin later in bid to rescue the deal.
"The situation on the ground is very fragile and complicated," he said.
Moscow, a staunch ally of President Bashar al-Assad, said Damascus resumed its assault on Aleppo after rebels violated the ceasefire.
Foreign Minister Sergei Lavrov said Moscow expected rebel resistance in the city to end in the next "two to three days".
Rebels and a source close to the regime told AFP that the evacuation had been suspended after objections from the Syrian government.
The source said Damascus objected to the number of people leaving, claiming rebels had sought to raise it from 2,000 to 10,000.
But Yasser al-Youssef, a political official from the Nureddin al-Zinki rebel group, said the regime and its ally Iran were trying to add "new conditions" to the agreement.
"They want to link this deal to other issues, including the areas of Fuaa and Kafraya," he added, referring to two government-held Shiite-majority villages in northwestern Syria that are under rebel siege.
Turkey too accused Assad's regime and its supporters of blocking the deal.
French President Francois Hollande joined Washington's call for international observers to be sent in to oversee the evacuation.
Hollande said those trapped by the fighting should "be evacuated in a dignified and safe manner, under the supervision of international observers and in the presence of humanitarian organisations."
Before the fighting resumed, crowds of civilians could be seen gathered in the streets of rebel areas from the early hours, some clutching bags of belongings, to await evacuation.
Some had slept in the open, despite the cold and a fierce storm that brought heavy rain and high winds.
Many were hungry, after weeks without regular meals because of dwindling food supplies caused by the army's siege.
The evacuation deal was announced a month into an army operation that has seen the government take more than 90 percent of the former rebel stronghold in east Aleppo.
Turkey, which has backed the opposition, said those leaving would be taken to Idlib province, which is controlled by a powerful rebel alliance that includes Al-Qaeda's former affiliate Fateh al-Sham Front.
The agreement came amid international concern about the plight of civilians in the city, and as the UN said it had reports of atrocities being committed by advancing government forces.
The UN has expressed concern over allegations that men have gone missing after crossing to government areas, and on Tuesday said it had credible reports of at least 82 civilians, including 11 women and 13 children, being executed in recent days.
Aleppo, a cultural and economic hub second only to Damascus in importance, had been split between a rebel-controlled east and government-held west since 2012.
It was unclear how many civilians remained in rebel territory, after an estimated 130,000 fled to other parts of Aleppo during the government advance.
More than 465 civilians, including 62 children, have died in east Aleppo during the assault, the Observatory said Wednesday in a new toll.
Another 142 civilians, among them 42 children, have been killed by rebel rocket fire on government-held zones in the same period, the monitor said.
More than 310,000 people have been killed since the Syrian conflict began, and over half the population has been displaced, with millions becoming refugees.
Assad's regime has enjoyed strong support from Iran as well as Russia and on Wednesday officials in Tehran hailed the "liberation" of Aleppo.
Yahya Safavi, top foreign policy adviser to supreme leader Ayatollah Ali Khamenei, said impending victory in Aleppo showed that "Iran is the leading power in the region."