The US president Barack Obama says the world is in horror at the Syrian regime's assault on the city of Aleppo.
The United Nations believes tens of thousands of people are still trapped in the east of the city after an operation to take anti-government supporters out of the area was suspended.
It is hoped the evacuations can resume this morning.
President Obama says the world cannot simply look away.
He said: "The Syrian regime, and its Russian and Iranian allies are trying to obfuscate the truth.
"The world should not be fooled, and the world will not forget."