A cease-fire negotiated overnight between Russia, Syria, Turkey and Syrian rebel forces appeared to holding on December 14 but a planned evacuation of rebel fighters and civilians from Aleppo was delayed.
Rebel officials said Iranian militias or other pro-Damascus Shi'ite forces were obstructing the departure of people from opposition-held districts of eastern Aleppo under a deal that will hand control of the area to the government.
Officials in the military alliance fighting in support of President Bashar al-Assad could not immediately be reached for comment. Assad has been backed by an array of Shi'ite militias from Iran and Lebanon in his campaign for Aleppo.
Diiffering times had been given for the start of the evacuation. Opposition officials said they had expected a first group of wounded people to leave late on December 13.
A military official in the pro-Assad alliance had said the evacuation would start at 5 a.m. local time on December 14.
But the Syrian Observatory for Human Rights said no fighter or civilian had left as that deadline passed.
A couple dozen buses were seen parked with their engines running on a main road out of the city, awaiting the evacuees. Another dozen were counted nearby.
Based on reporting by Reuters, AFP, and dpa