Civilians stay up all night awaiting evacuation but buses fail to leave as shelling of rebel-held territory resumes.

Syrian government forces renewed shelling on the last holdouts of rebel-held eastern Aleppo, raising fears that a deal to evacuate civilians and fighters from the devastated city may not be honoured.

“There is artillery [being fired] now … as I speak,” Zouhir Al Shimale, a journalist in east Aleppo, told Al Jazeera in a WhatsApp message on Wednesday.

“There aren’t any clashes,” he said, explaining rebel groups were not fighting at the moment. “There are injuries, but we don’t know how many. We can’t go outside because the shelling is indiscriminate.”

The UK-based Syrian Observatory for Human Rights also said shelling could be heard, but its origin was not clear. Speaking to Reuters news agency, rebel commanders said government forces had renewed shelling and violated a ceasefire reached a day earlier.

Medical sources told Al Jazeera cluster munitions were used in al-Zubdiyeh neighbourhood and elsewhere in the remaining rebel-held areas.

The Russian defence ministry confirmed government forces resumed attacks, claiming rebel groups broke the ceasefire in early Wednesday, according to Russia’s Interfax news agency.

Aleppo, once Syria’s bustling commercial hub, had been largely divided between a government-held west and a rebel-controlled east since 2012. But government forces are now in control of almost the entire city after weeks of intense fighting and relentless air raids.

Pounding the east of #Aleppo with dozens of artillery bombs since one hour until now we have counted more than 100 bombs.#Stand4Aleppo pic.twitter.com/1EG68WdpQV — Zouhir Al-Shimale (@ZouhirAlShimale) December 14, 2016

On Tuesday night, it was announced a ceasefire between the Syrian government and rebel groups would allow for the evacuation of tens of thousands of residents from the last pockets of rebel-held eastern Aleppo to the Idlib area or to Turkey.

The deal was brokered by Turkey and Russia.

READ MORE: Battle for Aleppo – ‘The sound of bullets doesn’t stop’

The arrangement was delayed on Wednesday morning, though, with rebel groups claiming a government-aligned Shia militia had turned back evacuees and demanded rebel-imposed sieges of the Shia majority towns of Kafraya and Fua were first lifted.

“Iran rejected the deal and hasn’t allowed the city to be evacuated. It has also laid down some conditions of its own,” Abdul-Mumin Zeineddin, a coordinator for the armed opposition in Aleppo, told Anadolu news agency.

“We will fight on until victory or death,” he added.

‘Massacred in cold blood’

Explaining that civilians were scared the evacuation could be delayed further, Shimale said: “No one knows what the regime will do.”

“People here are shocked [by the delay],” Shimale said. “We didn’t sleep last night waiting to leave.”

Russian Foreign Minister Sergey Lavrov said he expected the last of the “rebel resistance” to end within two to three days.

In what appeared to be a separate development from the planned evacuation, the Russian defence ministry said 6,000 civilians and 366 fighters had left rebel-held districts of Aleppo over the past 24 hours.

Buses evacuating people from rebel-held eastern Aleppo were allegedly turned around by Shia militias [Omar Sanadiki/Reuters]

Fears have been growing for thousands of trapped civilians as rebels make a desperate last stand in their remaining pocket of territory.

Late on Tuesday, Turkey’s Deputy Prime Minister Mehmet Simsek announced his government was planning to set up a new tent city to host “80,000 people fleeing eastern Aleppo”. He did not specify whether the facility would be in Turkey or Syria.

The UN said on Tuesday it received reports about pro-government forces executing scores of civilians in Aleppo, including women and children.

Eighty-two people were reportedly killed when Syrian forces took over rebel-held areas, it said.

Marwan Kabalan, a Syria analyst and associate political analyst at the Doha Institute, said the ceasefire breach may signal growing differences between Russia and Iran.

“The Russians seem to be bowing to international pressure in order to make the truce hold,” he told Al Jazeera.

READ MORE: After Aleppo’s fall – ‘Nobody can claim victory’

“It’s clear the Iranians have a different opinion here … I think they believe that they are winning and must finish off the opposition, rather than allow them to leave the city alive. The Syrian regime seems to be closer to the Iranian position,” he said, describing eastern Aleppo’s fall as a “major blow” to opposition forces.

A military media unit run by the Syrian government’s ally Hezbollah said on Wednesday talks were still taking place over a deal to evacuate fighters from Aleppo, and if government demands were not met, the deal would be off.

Syria’s conflict started as a largely unarmed uprising against President Assad in March 2011. It has since morphed into a full-scale civil war that has killed hundreds of thousands and left more than half the country’s prewar population displaced.

Efforts to negotiate a lasting resolution between the Syrian government and rebel groups have collapsed several times.

With reporting by Patrick Strickland