Thousands expected to be evacuated in Syria after blast

In Syria, more than three thousand people are expected to be evacuated on Sunday from four areas as part of a population transfer.

It was not immediately clear whether further evacuations were taking place on Sunday.

Assad holds the military advantage over the opposition in the west of the country thanks to Russia's intervention in 2015, although the insurgents continue to fight back and have made gains in some areas.

In return, the government will allow rebels and their families to leave the rebel-held towns of Madaya and Zabadani in northern Damascus to reach Idlib province. All four have been under siege for years, their fate linked through a series of reciprocal agreements that the United Nations says have hindered aid deliveries. Residents from the two villages had been evacuated Friday, along with more than 2,000 from Madaya, an opposition-held town outside of Damascus besieged by government forces.

A senior opposition official said 20 fighters who guarded the buses were killed as well as dozens of passengers. Abdurrahman said no permission was given for the evacuation to go ahead while Mahmoud said it has been delayed for "logistical reasons".

It was unclear who carried out Saturday's bombing attack.

At least 126 people, including 68 children, were killed Saturday in a suicide vehicle bomb attack on buses carrying Syrians evacuated from two besieged regime-held towns, a monitoring group said Sunday. White Helmets member Ibrahim Alhaj said the 100 fatalities documented by the rescuers included many children and women, as well as fighters.

There was no immediate claim of responsibility for the bombing, though the key Ahrar al-Sham rebel group denied any involvement.

On Saturday, a bomber targeted the buses as they waited in the militant-held al-Rashidin district on the outskirts of Aleppo to cross into government-controlled territory.

Residents of Madaya and Zabadani, formerly summer resorts, joined the 2011 uprising against President Bashar Assad.

"They were residents of two besieged Shia minority villages, who'd been besieged by rebels for years".

Critics say the string of evacuations, which could see some 30,000 people moved across battle lines over the next 60 days, amounts to forced displacement along political and sectarian lines.

Airstrikes by the US -led coalition had killed dozens of civilians over the past several weeks as the battle against the extremists intensifies in Syria and Iraq.