BEIRUT, Lebanon — Artillery shelling resumed early Wednesday on besieged eastern neighborhoods of the Syrian city of Aleppo, delaying the evacuation of thousands of civilians and medical staff members who had been expecting to leave under a deal involving Russia and Turkey.
It was the latest, bitter whiplash for those trapped in the ruined city. Under a supposed deal announced on Tuesday by Turkey, Russia and Syrian rebels, the last remaining fighters were to evacuate to rebel-held territory, and civilians were free to join them or to move to government-held areas. As a result, the whole city of Aleppo would be in the hands of forces loyal to President Bashar al-Assad.
A doctor, Imad Said, wrote in a Facebook post that he had performed surgery on a severely wounded boy and had later gone to look for the child’s family — only to find that they all appeared to have died.
A radiology nurse in Aleppo, Mohamed al-Ahmad, said he hoped the world would hear “our final scream from the last free neighborhoods in Aleppo.”
He said he had lost faith as the deal to evacuate the last pockets of opposition-controlled areas had fallen apart. “The agreement has been broken,” he said on Wednesday on the Viber messaging app. “Hundreds of shells have fallen on us. People who were supposed to leave were attacked. The medical situation is so dire situation that people are bleeding to death in the streets.”
On Wednesday, buses that were supposed to evacuate some of the last holdouts in the heavily bombed neighborhoods left, empty, after waiting for hours, the Lebanese television station Al Manar, which is affiliated with the militant Shiite group Hezbollah, reported.
The Pan-Arab television network Al Mayadeen showed buses idling at a prearranged evacuation point, waiting to take 5,000 fighters and their families to Atareb, a town west of Aleppo.
Osama Abu Zayd, a legal adviser to Syrian opposition factions, told The Associated Press that the evacuation deal was being resisted by Iran’s field commander in Syria. The Syrian Observatory for Human Rights, a monitoring group, said it believed that Iran — a major ally of the Syrian government — had balked at the deal, annoyed that Russia and Turkey had not consulted it.
Witnesses said pro-government militias had prevented a convoy of about 70 wounded people — mostly fighters and their relatives — from departing. The militias, observers said, insisted that they would not allow anyone out until rebel groups had ended their siege of Fouaa and Kfarya, two encircled Shiite enclaves in Idlib Province.
The Russian Defense Ministry blamed the rebels for the impasse, saying on Wednesday that they had “resumed the hostilities” at dawn, trying to break through Syrian government positions to the northwest.
The impasse could be the sign of a stalling tactic by Syria’s president, Bashar al-Assad. His government has often skillfully played its backers — Iran, Russia and others — against one another. The disagreement could provide cover for what the Syrian government has wanted to do all along: finish off the enclave with force. As one Syrian military officer told Reuters in Aleppo recently, rebels must “surrender or die.”
Malek, an activist who has repeatedly moved around eastern Aleppo for his safety, and who asked to be identified only by his first name for fear that he would soon find himself in government territory, said he had looked forward to the evacuation, but that “nothing happened.”
Interviewed over the messaging service WhatsApp, he added, using a mournful idiom, “We didn’t taste the flavor of life.”
Troubles carrying out the accord were not surprising, as there was no international monitoring — United Nations officials said the Syrian government had refused their repeated pleas to observe the process — and no mechanism to enforce the agreement. That has been a problem with other deals reached during the conflict.
At the United Nations on Tuesday, Secretary General Ban Ki-moon said there had been “credible reports” of atrocities, including extrajudicial killings, while eastern Aleppo was retaken.
Mr. Ban said the world body had been unable to verify the reports, however, because the Syrian government had repeatedly denied United Nations staff members the access required to monitor the evacuations and to aid civilians.
“As the battle for Aleppo concludes, I call on the Syrian authorities and their allies, Russia and Iran, to honor their obligations under international humanitarian law and do the following: urgently allow the remaining civilians to escape the area and facilitate access for all humanitarian actors and the delivery of critically important assistance,” he said. “The laws of war and universal human rights must be respected.”
Samantha Power, the United States ambassador to the United Nations, directed her remarks at officials of Syria, Iran and Russia, asking on Tuesday, “Is there literally nothing that can shame you?”
Her Russian counterpart, Vitaly I. Churkin, retorted that Ms. Power spoke as if she were Mother Teresa. He said that Russia had investigated claims of “ill treatment” of civilians and had found “not a single fact.”
In eastern Aleppo, residents expressed alarmed as Russian news agencies broadcast remarks from the Russian foreign minister, Sergey V. Lavrov, who said he expected the rebels to “stop their resistance within two, three days.” Those remarks alarmed observers, as the evacuation deal says rebels had already agreed to stop fighting in exchange for being allowed to leave.
“They are planning to slaughter us all,” said Monther Etaky, a civilian activist who said he had been hoping to evacuate.
Salem, a dentist who had kept his clinic open until last week, and who finally moved to one of the last rebel neighborhoods when his own was taken by government forces, said he could hear heavy shelling.
“We slept a quiet night, but sadly the shelling is back,” he said Wednesday morning, asking to be identified only by his first name. “Please share my message: The cease-fire collapsed. The situation is bad again.”
The evacuation plan came after two weeks of rapid advances by the Syrian Army and its allies, who drove insurgents into an ever-smaller pocket of eastern Aleppo, with support from heavy airstrikes and artillery fire.
Rebel groups have received support from Turkey, the United States and Persian Gulf states, but far less than the direct military aid that Iran and Russia have provided to Mr. Assad.