UPDATE 9.25am

Syrian rebel officials say a ceasefire deal for Aleppo is back on track, and its implementation, including evacuations from the last rebel-held areas of the city will begin “within hours”.

“An agreement has been reached and within the coming hours its implementation will begin,” Abdul Salam Abdul Razak, a military spokesman for the Nour al-Din al Zinki group, told Reuters.

He said the deal included the evacuation of people from two villages besieged by rebels in Idlib province, a condition introduced by the government side for the truce deal, which stalled on Wednesday amid heavy fighting in Aleppo, to resume.

An official in the pro-Damascus military alliance confirmed the truce deal was on, and said some 15,000 people would be evacuated from the villages, Foua and Kefraya, in return for the evacuation from Aleppo of “militants and their families and whoever wants to leave among civilians”.

UPDATE 5am

Syrian insurgents have launched counter–attacks against government forces in Aleppo, a rebel official has told Reuters.

Fighting is raging on as the truce deal collapses.

Zakaria Malahifji of the Fastaqim group said his men “have begun a military action” from their last remaining areas of control in the city.

#BREAKING #Rebels regain control of the #Alhaj Bridge neighborhood in #Aleppo, besieged and trying to advance toward #AlFardous Residences

— Step Plus (@stepplusone) December 14, 2016

The Syrian Observatory for Human Rights monitoring group and a witness reported that insurgents had staged a car bomb attack southwest of the historic Old City.

EARLIER

A ceasefire in the besieged city of Aleppo has been broken less than a day after it was struck, extending the pain for those living in the long-suffering city and plunging the civil war into fresh turmoil.

The Syrian Observatory for Human Rights initially said an explosion was heard in the rebel-held Saif al-Dawleh district on Wednesday night (AEDT). It then said heavy clashes including shelling and gunfire were raging once more in Aleppo.

“The clashes are violent and bombardment is very heavy … it seems as though everything [the ceasefire] is finished,” said Rami Abdulrahman, director of the British-based monitoring group.

Aleppo media activist Mahmoud Raslan also reported he was working for a Turkish agency in the city when a rocket crashed beside him.

The BBC reported heavy fighting in eastern Aleppo, including tank fire and up to 40 people seen injured.

It was unclear whether the Syrian military or rebel forces resumed the bombing first.

The latest development comes just hours after Russia’s Ambassador to the United Nations, Vitaly Churkin, told an emergency meeting of the UN Security Council that “military actions in eastern Aleppo are over”.

The United Nations announced at least 82 civilians had been killed by either Syrian or Iraqi forces in the final push to take Aleppo from anti-government rebels.

These included women and children, and it was feared there would be many more civilian casualties.

UN humanitarian spokesman Jens Laerke described the killings as ”a complete meltdown of humanity in Aleppo”.

https://twitter.com/saradarabi2012/status/809078421288615941

Since Russian airstrikes began on the city in July, pro-government forces had trapped thousands of civilians and rebel gunmen in eastern Aleppo under a crushing bombardment.

This escalated in recent weeks as they pushed to clear the northern city of the opposition. A final push by the Syrian government to retake Aleppo had seemed inevitably successful on Tuesday.

Thousands of civilians have died in Aleppo since fighting began in 2011. Photo: Getty

Buses that had arrived in Aleppo to take rebel forces, their families and civilians to safety left the city on Wednesday morning (local time) and returned to their depots as the ceasefire appeared to crumble.

The Lebanese channel al-Manar TV broadcast footage showing the Syrian government’s green-coloured buses leaving the evacuation point without passengers.

The buses’ departure could signal a major delay in the evacuations and even the collapse of the ceasefire deal.

Aleppo has been pummelled by Syrian government forces, with rebels fighting back. Photo: Getty

Shelling and rocket fire also resumed on Wednesday at the edges of the opposition’s enclave in Aleppo.

As evacuation plans faltered, UN war crimes investigators warned the Syrian government has the main responsibility for preventing any attacks and reprisals in eastern Aleppo, and it must hold to account any troops or allied forces committing violations.

In a statement, the United Nations Commission of Inquiry said “numerous reports” of violations by pro-government forces continued to emerge, including summary executions, arbitrary arrests and enforced disappearances.

The investigators had also received allegations of rebel groups, including Jabhat Fatah al-Sham, formerly Jabhat al-Nusra, and Ahrar al-Sham preventing civilians from leaving the area and of fighters embedding themselves within the civilian population, increasing the risk to civilians.

Despairing residents who are still managing to send messages on social media have turned from pleas of help, to messages of farewell.

https://twitter.com/L00n7/status/809061355378577408

https://twitter.com/Princess_Islam7/status/809053743593365504

Assad & Iranians broke the ceasefire. the genocide still ongoing!
No one could leave the city#StandWithAleppo#Aleppo pic.twitter.com/bgPYPPjvgI

— Quran and Hadith (@QuranAndHadithh) December 14, 2016

Meanwhile Turkey says it is still trying to broken a deal between Iran, Russia and the US to end fighting and to secure evacuations through a humanitarian corridor from the city.

Iran, another key Assad backer alongside Russia, was said to have imposed new conditions on the truce deal which were delaying its implementation.

The Syrian civil war has raged since 2011 when demonstrations against the President Bashar al-Assad government turned violent.

Mr Assad’s forces began shelling and shooting demonstrators, prompting anti-government rebels to fight back.

Aleppo, Syria’s most populous city and economic capital, became central to the civil war, with the west of the city controlled by the government and the east by rebels, following a rebel-initiated insurgency in 2012.

Russia was then called in to support the Syrian government with airstrikes in October 2015 and the tide began to turn against the rebels.

From July this year, the complete rebel loss of Aleppo seemed assured.

– with AAP