Deadly clashes erupted in Syria's Aleppo on Wednesday (December 14th) as a deal for the evacuation of opposition areas was put on hold, AFP reported.

The first departures had been expected around 5 a.m., but there was no movement, and a few hours later, fierce fighting shook the city.

The Syrian Observatory for Human Rights reported "very intense clashes on every front line".

The UN has expressed concern over allegations that men have gone missing after crossing to regime-held areas, and on Tuesday said it had credible reports of summary executions by pro-regime fighters.

UN rights office spokesman Rupert Colville described reports of at least 82 civilians, including 11 women and 13 children, being executed in recent days.

Meanwhile, the UN's Commission of Inquiry for Syria said Wednesday it had received reports that opposition fighters were blocking civilians from fleeing Aleppo, using them as human shields. It specifically implicated al-Nusra Front, now known as Fatah al-Sham Front, and Ahrar al-Sham opposition group.