Gunmen burn buses, Aleppo convoy goes through

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• Syrian rebels vow to resist army advances in Aleppo

The Syrian Observatory for Human Rights, a Britain-based war monitor, said the evacuation of the villages near Idlib had been postponed as a result of the incident. Five buses leaving Aleppo were held, packed with evacuees, for hours before they could drive the 5 km (3 miles) to rebel-held territory outside.

In return for the evacuation of fighters, their families and other civilians from Aleppo, the mostly Sunni insurgents had agreed that people in the villages of al-Foua and Kefraya, Shi'ite villages that they have besieged near Idlib, should also be allowed to leave.

A man on a motorcycle drives past burning buses while en route to evacuate ill and injured people from the besieged Syrian villages of al-Foua and Kefraya, after they were attacked and burned, in Idlib province, Syria December 18, 2016. REUTERS/Ammar Abdullah

Videos posted on social media showed bearded men with guns cheering and shouting "God is great" after torching the green buses before they were able to reach the villages.

State media said "armed terrorists", a term it uses for all groups fighting President Bashar al-Assad, had carried out the attack. Pro-Damascus Mayadeen television and the Observatory blamed the rebel group formerly known as the Nusra Front.

Rebel officials said an angry crowd of people, possibly alongside pro-government "operatives", was responsible.

Although the Aleppo evacuation convoy was eventually cleared to drive to rebel-held al-Rashideen, there was no official word on what impact the bus burning would have on the departure of more convoys from the city and the two villages.

While the Observatory said the convoy of five buses had reached al-Rashideen, a United Nations official in Syria said only that they had left east Aleppo, adding: "The evacuations are on".

Robert Mardini, regional director for the International Committee of the Red Cross (ICRC) which is at the forefront of the operation, tweeted that the buses and one ambulance of the Syrian Arab Red Crescent "just left dark & cold E #Aleppo", adding: "Hopeful operation will proceed smoothly."

Russian President Vladimir Putin, Assad's main foreign backer, and Turkish President Tayyip Erdogan, the rebels' main supporter, agreed by telephone on Sunday that the disruptions must be quickly overcome, sources in Erdogan's office said.

The commander of forces allied to Assad said there was still a chance for states with influence over rebel groups to find a way to evacuate civilians safely.

In a statement carried by a military news outlet run by Damascus's ally, the Lebanese group Hezbollah, the allied forces leadership said responsibility for the delay in the evacuation falls with "terrorists and their state sponsors".

Some 40 km (26 miles) to the northeast, hundreds of fighters and their families in Aleppo sat or stood in buses, hoping the evacuation would resume after a three-day hiatus.

Syrian state television, citing its correspondent in the city, said buses had started to leave east Aleppo where over 15,000 people had gathered in a square to wait, many after a night sleeping in the streets in freezing temperatures.

Aleppo had been divided between government and rebel areas in the nearly six-year-long war, but a lightning advance by the Syrian army and its allies began in mid-November following months of intense air strikes, forcing the insurgents out of most of the rebel-held territory within a matter of weeks.