US Secretary of State John Kerry has accused the government of Syrian President Bashar al-Assad of carrying out "nothing short of a massacre" in Aleppo.
Kerry, speaking at a news briefing, said the United States was seeking an immediate, verifiable, and durable cessation of hostilities in Aleppo, and said it appeared that air strikes and shelling had stopped and that convoys were moving out.
But there were also reports that a convoy of injured people had been fired on by Syrian government forces and their allies, Kerry said.
Activists and residents inside the remaining rebel enclave said this week that pro-government militias had summarily executed dozens of civilians.
"There is absolutely no justification whatsoever for the indiscriminate and savage brutality against civilians shown by the regime and by its Russian and Iranian allies over the past few weeks, or indeed over the past five years," Kerry said.
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"We are seeing the unleashing of a sectarian passion."
He added: "The Assad regime is actually carrying out nothing short of a massacre."
Kerry, speaking in the waning weeks of the Obama administration, reiterated long-standing US policy on Syria, and called on the international community to exert pressure on all parties in the nearly six-year-long civil war.
Five years of international efforts aimed at reaching a peace deal failed.
Backed by Russia and Iran, Assad's government has vowed to fight until he has regained full control of the country.
Its takeover of Aleppo, the most populated city in Syria before the war, would mark a major victory for Assad.
