U.S. President Barack Obama charged that Russia, Iran, and Syria have "blood on their hands" from their brutal takeover of Aleppo even as he lamented being unable to stop the bloodshed in Syria despite years of effort.
"The world as we speak is united in horror at the savage assault by the Syrian regime and its Russian and Iranian allies on the city of Aleppo," Obama told a yearend news conference on December 16. "This blood and these atrocities are on their hands."
"We have seen a deliberate strategy of surrounding, besieging, and starving innocent civilians. We've seen relentless targeting of humanitarian workers and medical personnel, entire neighborhoods reduced to rubble and dust. There are continuing reports of civilians being executed."
Obama in particular warned Syrian President Bashar al-Assad, whose civil war against armed opponents since 2011 has killed more than 250,000 people, that he will not be able to "slaughter his way to legitimacy."
But at the same time, Obama acknowledged the United States and its allies have had little success in their attempts to prevent the bloodshed or alleviate it, mostly as a result of his decision early in the war not to get in involved militarily.
"For years, we've worked to stop the civil war in Syria and alleviate human suffering.... It has been one of the hardest issues that I've faced as president," he said.
Obama said he concluded early on there was no way for the United States to intervene militarily "on the cheap."
"Unless we were all in and willing to take over Syria, we were going to have problems," he said, adding that a military takeover would have required "putting large numbers of U.S. troops on the ground, uninvited, without any international law mandate."
Obama also acknowledged that his administration's efforts to establish a peace process through the United Nations as well as directly in negotiations with Russia have borne little fruit.
"I cannot claim that we've been successful, and so that's something that, as is true with a lot of issues and problems around the world, I have to go to bed with every night," Obama said.
"But I continue to believe it was the right approach given what realistically we could get done."
Many analysts say western inaction led to Russia's decision last year to intervene. Moscow is now helping Assad's regime make significant gains retaking rebel-held territory.
As the president spoke, Russia and Syria had halted their evacuation of thousands of civilians and fighters as they moved to take control of the last areas of Aleppo once held by rebels.
Obama threw his weight behind a French initiative at the United Nations to authorize UN observers to monitor the evacuation -- but Russia has blocked such moves and UN officials seem as confounded as Obama on how to proceed.
Outgoing UN Secretary-General Ban Ki-moon said at his final news conference on December 16 that the Syrian war has been "heartbreaking" for him, especially since efforts to evacuate hundreds of wounded civilians stopped on December 16.
"The carnage in Syria remains a gaping hole in the global conscience," he said. "Aleppo is now a synonym for hell."
Ban urged "the parties to take all necessary measures to allow safe resumption of this evacuation process."
Syrian forces said they stopped evacuations because rebel groups had not made good on promises to similarly evacuate wounded government troops and civilians from two Shi'ite villages the rebels are besieging in Idlib Province.
Iran demanded that the villages be included in a cease-fire deal which has enabled people to leave Aleppo, UN officials have said.
Turkey, a main backer of the rebels, said Ankara is talking to counterparts in Tehran to try to resume the evacuations.
Obama dismissed claims by Russia and Syrian officials that all innocent civilians who were trapped in Aleppo had been able to leave already.
"Humanitarian organizations who know better and who are on the ground have said unequivocally that there are still tens of thousands that are trapped and are prepared to leave," Obama said. "So right now our biggest priority is to get them out."
U.S. Ambassador to the UN Samantha Power sought to address Russian resistance to installing UN observers to monitor the evacuations.
"Russia has helped deliver Aleppo to the Syrian government. Surely Russia can secure actual safe corridors for civilians," she said.