Explosions have been heard near the staging area where convoys of buses are leaving war-torn Aleppo with evacuees, an eyewitness says.
A Syrian official says the evacuation of the eastern neighbourhood has been suspended due to “obstructions”.
There were unconfirmed reports of “sounds of bombings” near the staging area and shootings in an area controlled by forces loyal to President Bashar al-Assad.
A media outlet run by Assad ally Hezbollah claimed rebels shot at an evacuation checkpoint in the suburb of Ramouseh, while pro-opposition sources claimed the regime fired at the convoy.
There were also claims by Syrian state TV station al-Ikhbariya that rebels had sought to take prisoners with them during the evacuation, breaching a deal that was brokered along with a shaky ceasefire with help from Russian and Turkish officials.
Thousands of people have gathered in the streets of Aleppo as they flee the devastated city after Syrian government forces made rapid advances on the last rebel-held enclave in recent days.
There are desperate scenes amid bombed-out buildings and rubble, as wounded rebels and civilians, including many women and children, queue to flee the city and gather near fires to stay warm in the freezing weather.
Thousands of people have been evacuated since the massive humanitarian effort began on Thursday, and thousands more are waiting.
Many were so anxious to leave they decided to make the dangerous journey in private cars.
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