The long-awaited evacuation of residents of besieged Syrian towns has been postponed after a bombing which targeted a convoy of evacuees left more than 120 dead.
More than 3,000 people were expected to be evacuated from Foua and Kafraya, two mainly Shia towns in the northwest of the country besieged by the rebels, on Sunday as part of a larger swap with residents from two government-surrounded towns.
However, it was cancelled at the last minute without explanation.
Rami Abdurrahman, who heads the Britain-based Syrian Observatory for Human Rights, said the evacuation had been delayed because permission was not given by both sides.
It came a day after a blast hit a convoy of buses carrying residents from the two towns, who have lived for years under siege by extremist rebels, as they waited at a transit point in rebel-held Rashidin, west of Aleppo.
According to local reports, a man had lured children waiting near the buses over to a car with the promise of food. When several dozen had gathered a bomb was detonated, killing more than 80 children and 13 women.
Most of the dead and wounded were government supporters, as well as a few fighters who had been guarding the buses.
Maysa al-Aswad, a 30-year-old evacuee from Kafraya, said she was sitting on one bus with her six-month-old son Hadi and 10-year-old daughter Narjis when the blast shook the parked convoy.
"Hadi was on my lap and Narjis on a chair next to me. When the explosion happened I hugged them both and we fell to the floor," she said.
"All I can think about is how we survived all the death during the last few years and then could have died just after we finally escaped."
Both sides have blamed the other for the attack. However, both the Islamic State of Iraq the Levant (Isil) and the al-Qaeda-affiliated Fatah al-Sham Front have targeted civilians in government areas in the past.
Many of the residents still waiting for evacuation now fear reprisal attacks.
The evacuation deal, brokered by Qatar and Iran, sees thousands of government supporters in rebel-held Foua and Kafraya granted safe passage out in exchange for thousands of opposition supporters in the government-besieged towns of Madaya and Zabadani, in a complex population swap.
The fate of all four has been linked through a series of reciprocal deals known as the “four towns agreement”.
An estimated 70,000 people have been living under intense siege in the areas, where little food or aid has been allowed in since 2015.
Stephen O'Brien, United Nations relief coordinator, said on Sunday he was "horrified" by the deadly bombing, and that while the UN was not involved in the transfer it was ready to "scale up our support to evacuees."