A cease-fire in besieged eastern Aleppo appears to have fallen apart, blocking a planned evacuation of civilians and insurgents trapped in the war zone.

It's difficult to confirm exactly how many civilians remain in the small slice of Aleppo still controlled by rebel groups, but estimates put the number in the tens of thousands.

A cease-fire, essentially a surrender by rebel groups, was negotiated by Turkey and Russia and announced Tuesday. Under the agreement, civilians were supposed to be evacuated to safety, but that deal has collapsed.

"So far nobody has been evacuated," The New York Times reporter Anne Barnard tells NPR. "The first convoy that attempted to leave was stopped by the Iranian-backed Shiite militias that have been helping the Syrian government on the ground. It seems that Iran and the Syrian government were not pleased that Turkey and Russia struck a deal without them."

In addition to the evacuations being halted, warfare and shelling has also resumed in the region, The Associated Press reports:

"Syrian activists say fighter jets have resumed bombing raids over remaining rebel areas in eastern Aleppo, further imperiling a cease-fire deal for the city."Media activist Mahmoud Raslan says the aircraft bombed the rebel Ansari district in the city on Wednesday."He says that the aircraft 'began to strike as if there's no such thing as a "cease-fire" or "evacuation of civilians." '"Raslan says the bombing is a de facto announcement that 'they are going to kill us all.' "

Opposition-leaning monitoring group the Syrian Observatory for Human Rights says that shelling and airstrikes on eastern Aleppo have restarted, and rebel groups have also resumed shelling government-held territory, NPR's Alison Meuse reports.

There are conflicting accounts of who first violated the cease-fire, the BBC's Thomas Morgan says.

"Activists and pro-opposition media say regime-backed militia restarted the shelling of rebel areas this morning," he reports. "However, Russia's defense ministry says the fighting was initiated by the rebels, who used the cease-fire as an opportunity to regroup."

Those inside eastern Aleppo have described horrific bloodshed over the past few days. People told NPR there's no food, no fuel and no medical care available, and that the streets are filled with carnage. Various U.N. agencies have received reports of indiscriminate killing and children coming under fire.

The White Helmets, a volunteer civil defense organization, say they can no longer provide estimates of the body count in eastern Aleppo.

Abdulkafi Alhamdo, an opposition activist and English teacher who is still in besieged eastern Aleppo with his wife and young daughter, spoke with Alison about life in the city over the past few days.

"It was hell," he said. "The killing — you can just see bodies on the streets, you can hear their voices crying just to find someone to help.

"They gave us two choices only — leave or die," he said. "You leave your friends, you leave your house, you leave your history."

Thousands of civilians have already fled the rebel-held side of the city. Of those who remain, many are unwilling to enter government-held territory. As NPR's Alice Fordham reported yesterday, some are worried they will be sent to Syria's notorious prisons.

"They know that they are wanted by the government for activities like protesting or providing medical care to protesters or fighters, other activities that are viewed as terrorism by the government," Anne Barnard tells NPR. "It's actually easier in some cases for fighters to get amnesty than for civilians involved in these activities."

So the evacuation plan called for the civilians to be taken to Idlib province, which is held by rebels, instead of to government-controlled regions. From there, the civilians would be free to travel at will.

With that plan in tatters, it's not clear what will happen next.

Many in the bloody war zone were already bracing for death or capture. Civilians in eastern Aleppo were posting farewell messages on social media on Monday and Tuesday.

As we reported yesterday, Aleppo — once Syria's largest city, and a major commercial hub — has been divided between government and rebel forces for four years. In recent weeks, President Bashar Assad and his allies have waged an offensive to retake the entire city.

Re-taking Aleppo in its entirety is a significant symbolic and strategic victory for Assad, giving the government control of Syria's key cities along Syria's western spine, as NPR's Greg Myre explains on our Parallels blog.

"The Syrian leader can claim a stronger position than at any point since the early days of a war that broke out in 2011," Greg writes. "This doesn't mean Syria's bloodletting is over, but it is entering a new phase. ... what now looms is a more focused confrontation that features Assad's forces in heavily populated western part of the country, and the Islamic State in the sparsely populated deserts of the east."

The loss of Aleppo is also a devastating blow for moderate rebels in Syria's complex, many-sided war. Anne Barnard explains that in Aleppo, the majority of fighters were not affiliated with extremist Islamist groups like the Islamic State or the al-Nusra front.

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