Story highlights US envoy Samantha Power criticized Syria and Russia over Aleppo humanitarian crisis

Russia's UN ambassador said the West had no right to lecture

(CNN) Samantha Power, the United States ambassador to the United Nations, unleashed a scathing attack on Syrian President Bashar al-Assad and his allies on Tuesday.

Power slammed her Syrian, Iranian and Russian counterparts for the humanitarian crisis unfolding in Aleppo , in a speech at a UN Security Council Emergency Briefing on Syria.

"To the Assad regime, Russia, and Iran -- three Member States behind the conquest of and carnage in Aleppo -- you bear responsibility for these atrocities. By rejecting UN-ICRC evacuation efforts, you are signaling to those militia who are massacring innocents to keep doing what they are doing," Power said.

"Denying or obfuscating the facts, as you will do today -- saying up is down, black is white -- will not absolve you. When one day there is a full accounting of the horrors committed in this assault of Aleppo -- and that day will come, sooner or later -- you will not be able to say you did not know what was happening. You will not be able to say you were not involved. We all know what is happening. And we all know you are involved.

"Aleppo will join the ranks of those events in world history that define modern evil, that stain our conscience decades later. Halabja, Rwanda, Srebrenica, and, now, Aleppo.

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