Editor's Note: This story has been updated throughout.

Troops loyal to Syrian dictator Bashar al-Assad and foreign militias under Iranian command swept into eastern Aleppo on Monday, recapturing nearly all of the city’s opposition-held areas and seizing the citadel of the Syrian revolution.

The triumphal takeover followed a day of intense bombing of houses and apartment buildings, destroying so many that it was impossible to determine the death toll. The neighborhoods of Bustan al-Qasr, al-Kallasa, al-Farod and al-Salhin in the Old City, as well as Sheikh Saed, in the southern district, are all now under regime control.

The United Nation’s top human rights official on Tuesday charged the U.S. and other countries with collectively wringing their hands in the face of the “wanton slaughter of men, women and children” in Aleppo and pleaded for the world to take measures to protect those fleeing the Russian and Syrian regime onslaught.The U.N. had received credible reports of scores of civilians being killed either by intense bombardment or summary executions by pro-government forces. Zeid Ra’ad al Hussein, the High Commissioner for Human Rights, said in a statement.“Dozens of bodies reportedly litter the streets of a number of east Aleppo neighborhoods, with residents unable to retrieve them due to the intense bombardment and fear of being shot,” Hussein said. He added that the U.N. had reports that at least 82 civilians, including 11 women and 13 children in four neighborhoods – Bustan al-Qasr, al-Ferdous and al-Kallaseh and al-Saleheen.Decrying “the crushing of Aleppo, the immeasurably terrifying toll on its people, the bloodshed, the wanton slaughter of men, women and children, the destruction,” the Jordanian-born U.N. official warned, “We are nowhere near the end of this cruel conflict.”“What can happen next, if the international community continues to collectively wring its hands can be much more dangerous." Hussein said the slaughter in Aleppo could repeat itself in Douma, Raqqa and Idlib, referring to other opposition-held areas in the war-ravaged country.“We cannot let this continue.”The White Helmets, a volunteer rescue group, described Aleppo as being “like hell.” The streets and destroyed buildings “are full of dead bodies,” said a tweet by one of its volunteers. The rescue service was reported to be totally paralyzed by the assault.The head of the group’s Aleppo branch, Ammar al-Salmo, said on Al Jazeera television that many old men died of the cold weather in eastern Aleppo.More than 100 unaccompanied children were reported to be trapped in a building under heavy bombardment in eastern Aleppo, according to UNICEF, the U.N. agency responsible for child welfare said, quoting an unnamed doctor in the city, Reuters reported.The head of the Aleppo local coordinating committee told regime forces had captured the remaining food supplies in eastern Aleppo and there are no functioning bakeries and no bread, the Turkish Anadolu news agency reported.

Syrian army spokesman Brig. Gen. Samir Suleiman countered that the U.N. was lying.

"These are false claims. The Arab Syrian army can never do this and we have never done it in our army's history." Yesterday, the official Syrian news agency SANA instead lay blame for atrocities in Aleppo on the rebels, alleging that eight people were killed and 47 were injured in regime-held areas after the opposition bombed them. Most of the victims were women and children, according to the agency.

Abdullah Othman, the head of the Consultative Council in the Levant Front, one of the largest rebel groups in Aleppo, said this morning that the opposition was still in possession of six neighborhoods, including Salaheddine, once the sight of some of the fiercest urban combat the Syrian civil war had witnessed."Last night we were able to reinforce our new defense lines and to build some blast walls on the new borders," Othman told The Daily Beast today, speaking from the border town of Azaz. "Today the regime forces tried to sweep through our new defense lines but they haven’t been able to do so yet. But the problem is the barbaric, unprecedented bombardment and shelling that you can’t even imagine."

Civilians were apparently crammed into whatever buildings still remain in the tiny quarters yet to be recaptured by the Assadists, but many were left outside in the streets, owing to lack of space. It is here, in broad daylight, Othman said, that men, women and children were being cooked alive by barrel bombs dropped right where they stood.And those who survive the air raids could not be helped. "Women and children — their screams can be heard underneath the rubble. Unfortunately, there is nothing we can do to get them out. Everyone is panicking. There is great fear. Everyone can only think of himself, not about others."

Yesterday, some residents who couldn’t take the bombardment anymore fled toward regime controlled areas, according to Othman.

"Seventy-nine of them were executed at the barricades. The rest — everyone under 40 — were taken to warehouses that look more like internment camps. They face an unknown fate," he said."This morning 20 women committed suicide in order not to be raped."

The last hope of the besieged rebels, most of whom seem to have withdrawn in the face of certain defeat, had been to receive reinforcements or resupplies from their counterparts in the southern and western suburbs. That option has now been foreclosed upon as these routes are completely interdicted by the regime.

Enab Baladi, a Syrian opposition news channel, said regime artillery attacked the six neighborhoods remaining in rebel hands with 40 shells and its ground forces – mostly Shiite militias under Iranian command – are attacking from four directions.

***

Activists and residents of the ever-dwindling opposition pocket, an urban islet of about five square kilometers and home to as many as 100,000 people, spent the last 24 hours signing off from social media, asking journalists to tell their story, and warning of their impending demise.

The Daily Beast was able to get in touch with Abdulkafi Al-Hamdo, a university teacher in the besieged city, on Monday evening. The brief conversation was as follows:

TDB: “I hope you’re safe.”

AA: “I don’t think I will be tomorrow.”

TDB: “Do you expect all the remaining besieged neighborhoods will fall by tomorrow?”

AA: “No. Except over the body of every civilian. I won’t surrender my body, and my wife, and my daughter to the Assad regime without defending them… I hope that you’ll tell everyone what I’m saying.”

On a publicly visible WhatsApp feed belonging to the Aleppo Siege Media Center, al-Hamdo was more fatalistic. “Doomsday is held in Aleppo,” he said. “People are running don’t know where. People are under the rubble alive and no one can save them. Some people are injured in the streets and no one can go to help them [because] the bombs are [falling on] the same place.”

Award-winning blogger and activist Marcell Shehwaro, a native of Aleppo, shared on Facebook a message from one of her most “peaceful” and least-sectarian friends. “No Marcell, don’t worry,” it read. “I will kill myself, I won’t let them arrest me.”

Lina al-Shamy, a 26-year-old woman speaking in fluent English, posted a video of herself to Twitter.

“To everyone who can hear me. We are here exposed to a genocide in the besieged city of Aleppo. This may be my last video. More than 50,000 civilians who rebelled against the dictator, al-Assad, are threatened with field executions or dying under bombing. According to activists, more than 180 people have been field executed in the areas the regime has recently retook control of by Assad’s gangs and the militias that support them. The civilians are stuck in a very small area that doesn’t exceed two square kilometers. With no safe zones, no life, every bomb is a new massacre. Save Aleppo, save humanity.”

Jouad al-Khateb had a similar message—one hesitates to call it valedictory— for the world. In Arabic, he told the camera: “Behind me is the Bustan al-Qasr neighborhood. Since last night up to the present moment, it is being bombed with every kind of weapon; vacuum rockets, missiles. The rockets have not stopped since last night. The people coming out of Bustan al-Qasr are telling me it’s become a city of ghosts. More than 20 families remain under the rubble across various districts.” The White Helmets were unable to reach any of the victims, al-Khateb added.

“My message to those watching: Just stop the waterfall of blood for us. We don’t want to leave the besieged areas. Just stop the waterfall of blood. It’s as if this has become very normal for the international community, you know, a rocket falls, 20 or 30 people are killed, under the rubble, they can’t pull them out—that’s a totally normal thing. In any case, there’s no space for graves to bury them in. Let them be buried under the buildings. I think this will be my last video, because we’ve gotten bored of talking, bored of speeches.”

Al-Khateb was interrupted by a loud groaning sound.

“That’s a barrel bomb,” he said, referring to one of the regime’s most notorious improvised munitions, a metal canister filled with high explosives and shrapnel, which are dropped indiscriminately from helicopters.

Another trapped resident, Ameen al-Halabi, boasted on Facebook, “I’m waiting for death or imprisonment by the Assad forces. I would rather die on the soil of my land than be arrested by their faithless militias.” Al-Halabi asked his friends to forgive him if this was the last message he wrote.

On several rebel chat forums on the popular messaging application Telegram, there were calls for the youth of Syria to wage “jihad” against the conquerors of Aleppo, if only to defend the honor of women who had allegedly been raped in the course of the Assadist blitzkrieg.

Whether or not that particular war crime has yet occurred in Aleppo—though human-rights monitors have documented mass rape in Syrian regime prisons since the start of the conflict—the call for holy war against the regime may yet take hold. For this reason, the CIA and Joints Chiefs of Staff earlier advised the Obama administration that the fall of eastern Aleppo, apart from being a humanitarian catastrophe, would also constitute a counterterrorism threat to the United States. The radicalization of survivors is all but a foregone conclusion.

***

Those already radicalized have had a remarkably auspicious week. While the regime was focused on reclaiming Aleppo, ISIS, or the self-proclaimed Islamic State, was able to completely retake another ancient Syrian city, Palmyra, which it had lost, to much international fanfare, last March.

Despite the gravity of the day’s events, and the many breaches of international law that led to the collapse of the rebel-held area, U.S. political leaders were slow to comment. President Obama has watched in silence as Russia and the Assad regime have committed what Secretary of State John Kerry called crimes against humanity, and Donald Trump has not once publicly mentioned the word “Aleppo” on his favorite social-media platform, Twitter, since being elected president of the United States a month ago. Kerry even meekly invited the Kremlin over the weekend to show “a little grace” in how it recaptured eastern Aleppo.

Meanwhile, the leading Syrian political opposition group charged Russia and the Syrian air force with the deaths of at least 150 civilians in what it described as a sarin gas attack on several villages in rural eastern Hama province Monday, and a further 15 in a missile filled with the nerve agent on the city of Raqqa on Monday.Demanding an international investigation, the Syrian Coalition denounced what it called the “shameful international inaction, which has paved the way for the level of blatant criminality by the Assad regime and its allies.”The gas attack, if confirmed, may have been intended to stop ISIS from linking up their forces in the Homs desert to those in the Hama desert area.

***

“The Holy Quran teaches that whoever kills an innocent is as—it is as if he has killed all mankind. And the Holy Quran also says whoever saves a person, it is as if he has saved all mankind.”

So did Obama tell a receptive audience in Cairo, in 2009, in a much-scrutinized maiden speech of his administration. (The second line in this sacred allusion, as it happens, is also the mantra of the now-helpless White Helmets.)

In a letter addressed to U.S. Congress, a copy of which was obtained exclusively by The Daily Beast, the Levant Front's al-Othman beseeches legislators to "make one last effort to protect the civilians of Aleppo -- to achieve where we have failed -- by calling upon...Obama, to take strong and immediate measures for the people of Aleppo before the Assad murderers overtake us."

But it's likely too late. And so the president who came to office promising to repair the breach between the United States and the Islamic world, putatively caused by the war on terror and the invasion and occupation of Iraq, is now set to leave office having done little to stop to the slaughter or displacement of millions in Syria or the wholesale destruction of one of Islam’s most venerated cities.

—With additional reporting by Musab Al-H amadee