A leading U.N. humanitarian aid official for Syria says the United Nations hopes to begin medical evacuations from rebel-held eastern Aleppo during a "pause" in fighting on Friday.

Jan Egeland says the U.N. has received the "green lights" it needs from Syria's government, armed opposition groups and Russia, which announced the pause in fighting that began on Thursday.

Speaking in Geneva, Egeland also says the Russian government is considering a U.N. request to extend the planned three-day string of temporary, 11-hour daily pauses in fighting to a fourth day.

Egeland says the U.N. hoped to organize evacuations of "several hundred" critically wounded or sick people with their families either to government-controlled western Aleppo or to the rebel-held city of Idlib to the southwest, and deliver medical supplies to eastern Aleppo.