The residents of besieged east Aleppo have endured another day of uncertainty and fear as a truce and evacuation agreement hung by a thread, with negotiators racing to rescue a deal that could save tens of thousands of lives.

About 8,000 civilians had been evacuated from the shrinking patch of rebel territory but tens of thousands more were still trapped when the government of the Syrian president, Bashar al-Assad, suspended the pact, which was negotiated by Turkey and Russia.

The abrupt suspension resulted from the refusal of al-Qaida-linked militants to allow the evacuation of wounded civilians from Fua and Kefraya, two Shia villages in Idlib province that have been besieged by Islamist rebels for years and whose relief was part of the agreement, offered as a concession to Iran. Tehran-backed militias spearheaded the assault into east Aleppo.

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Also threatening the deal was the detention by pro-Assad militias of a convoy of 25 vehicles that was on its way out of the Aleppo enclave, accompanied by workers from the International Committee of the Red Cross and the Syrian Arab Red Crescent who are overseeing the evacuation.

“Today was another difficult day for the Aleppo people,” said one teacher who was still in the city. “We went there from 6am until 5pm. No bus was there.”

“I have to say it to the world: if they don’t save Aleppo now, they will not save it forever,” he added. “Aleppo is now without any kind of life. Aleppo now is the place of death. The world should do something.”

The UN Security Council could vote as early as this weekend on a French-drafted proposal to allow international observers in Aleppo and ensure urgent aid deliveries. US ambassador Samantha Power said after a closed-door council meeting that UN officials were ready to be sent quickly. “The presence of independent observers can deter some of the worst horrors,” she said.

Few residents in east Aleppo could be reached because of an apparent internet outage through most of the day, but those who were able to speak described scenes of chaos and thousands of families braving the winter cold to wait for hours for buses to take them out of their home city. Residents faced a choice of making a last stand against an overwhelming force led by Iranian-backed militias, or surrendering to those groups, who are accused by the UN of killing civilians in newly reclaimed areas.

Residents have lived for months under debilitating siege and airstrikes with dwindling food stocks and medicine and no functioning hospitals.

“The situation of the wounded who remain in Aleppo is horrible,” said one rebel fighter in the city. “No medicine, no disinfectants, nothing at all. The situation is tragic.”

Facebook Twitter Pinterest Residents gathering near green government buses for evacuation on Thursday. Photograph: Uncredited/AP

Sources with knowledge of the evacuation deal told the Guardian it had been suspended over the refusal of Jabhat Fateh al-Sham (JFS), a powerful al-Qaida-linked group, to allow the evacuation of wounded civilians from Fua and Kefraya.

But by the early afternoon, a senior rebel source said the al-Qaida affiliate had given its consent to the deal. Rebels in Idlib are part of a predominantly Islamist coalition, of which JFS is one of the most powerful.

Opposition activists accused the regime of detaining a convoy of 25 vehicles from Aleppo that left early in the morning, separating them from their Red Cross and Red Crescent escort, and shooting dead four people there. The allegations could not be independently confirmed.

If the evacuations of 400 wounded people from Fua and Kefraya were to go ahead as planned on Friday, it could allow the Aleppo evacuation to continue, hours after the agreement reached on Wednesday night appeared to be on the verge of collapse.

Buses and ambulances that had been waiting to evacuate more people had left the departure zone after gunfire and explosions were heard.

The Turkish president, Recep Tayyip Erdoğan, said the truce deal was the last hope for Aleppo’s civilians and urged both sides to abide by it.

“The Turkey-brokered truce in Aleppo and the continuation of evacuations is the only hope left for innocent people,” Erdoğan tweeted. “I urge all parties and the international community to abide by the truce agreement and support the implementation of the evacuation process.”

He added: “The people of Aleppo are not alone. We will do everything in our power to save innocent lives.”

In his final news conference before he steps down as UN chief on 31 December, Ban Ki-moon said Aleppo had become a “synonym for hell”. “The carnage in Syria remains a gaping hole in the global conscience,” he added.

A rebel source said negotiations were continuing to try to rescue the deal, but Iran was deliberately attempting to undermine it by demanding a “Christmas wishlist” of concessions that included handing over the bodies of Shia fighters, releasing prisoners of war, and a full evacuation of all of the inhabitants of Fua and Kefraya.

“The recent statements that you’re hearing from the Russians about the evacuation being over are false, they just lost control over the Iranians and they don’t want to look bad, so they’re saying the whole evacuation is over,” the source said, referring to an announcement on Russian state news agencies that the evacuation was complete, despite tens of thousands of civilians remaining in the enclave.

“Iranian militia, with the regime, are planning a massacre in east Aleppo and [of] the hostages,” the source added.

The delicate operation to evacuate remaining civilians and fighters from east Aleppo began on Thursday and continued through the night. Turkish government officials said about 8,000 people had left the city to go to rebel-held territory in the west of the province.

A ground assault to recapture all of Aleppo, led by Iranian-backed militias supporting Assad, began in mid-November and had overrun more than 90% of the former rebel bastion before the evacuation began.

The evacuation of the wounded from Fua and Kefraya was agreed after Iran blocked an initial ceasefire and evacuation deal that was negotiated on Tuesday night.

Russia said it would convene Syrian peace talks later this month to be attended by Iran and Turkey but none of the Gulf states or western powers. The Russian president, Vladimir Putin, said the talks on 27 December would complement rather than compete with the UN-led Geneva peace process, and were being convened on the basis of retaining Syria as a unitary state.

In a separate development on Friday, a girl blew herself up at a police station in the Midan neighbourhood in the capital, Damascus. The state-run Ikhbariya news channel showed blurred images of what looked like the blackened head of a girl in a blanket, and scenes of destruction. The Al-Watan newspaper, which is close to the government, said the suicide bomber was seven years old.

A witness in the area of the blast told Reuters a young girl entered the police station and, after asking to go to the toilet, blew herself up. The Syrian Observatory for Human Rights (SOHR) said there had been an explosion and that there were reports of casualties.

Additional reporting by Patrick Wintour