Medical evacuations planned in east Aleppo for Friday (October 21st) have been delayed, the UN said, after warring parties failed to give necessary security assurances, AFP reported.

"Medical evacuations of sick and injured could unfortunately not begin this morning as planned because the necessary conditions were not in place," said Jens Laerke, spokesman for the UN humanitarian office.

Emergency relief workers have so far been unable to deploy from positions in regime-controlled west Aleppo, he said, describing the situation as "astronomically difficult".

On Thursday, UN Secretary-General Ban Ki-moon told a special meeting of the General Assembly that bombing raids in Aleppo have left nearly 500 dead and about 2,000 injured, while food rations are running low.

More than a quarter of all deaths are children, he noted.

No UN aid convoy has entered Aleppo since July 7th, and food rations will run out by the end of October, Ban warned, saying hunger was being used as a weapon of war.

On Friday, the UN human rights council opened a special session on Aleppo, with rights chief Zeid Raad al-Hussein demanding action against "crimes of historic proportions".

Calling Syria's more than five-year civil war "a proxy conflict", Zeid urged parties to the fighting to set aside "global gamesmanship".