Syria has strongly denounced a deadly Takfiri bomb attack on buses carrying people from two Shia-majority villages in the northwestern province of Idlib, calling on the United Nations to hold responsible the countries that fund terrorists and provide them with weapons and ammunition.
The families were forced to wait for more than 28 hours to cross into government-held areas.
There was no immediate claim of responsibility for the attack, which pro-government media said was carried out by a suicide vehicle bomber.
Maysa, a 30-year-old evacuee from Kafraya, said she was sitting on one of the buses with her six-month-old son Hadi and 10-year-old daughter Narjis when the blast shook the parked convoy.
The reasons for the delay were not immediately clear.
A suicide bomber lured children by handing out crisps before detonating a huge blast that killed at least 45 people in Syria, a witness said.
The deal, recently reached between the rebels and the government under the supervision of Iran, Turkey and Qatar, was created to secure evacuation of the people from the pro-government Shiite towns of Kafraya and Foa in Idlib province toward government areas in Aleppo province.
An opposition activist group and a TV station run by Lebanon's Hezbollah say more than 3,000 people are expected to be evacuated from four villages as part of a population transfer that was briefly stalled by a deadly blast that killed scores.
"The situation is disastrous", said Ahmed Afandar, a resident evacuated from the opposition area near Madaya. White Helmets member Ibrahim Alhaj said the 100 fatalities documented by the rescuers included many children and women, as well as fighters.
The blast hit the Rashidin area on Aleppo's outskirts, where dozens of buses carrying mostly Shi'ite residents of two villages that are being evacuated in a deal between warring sides were waiting to enter the city.
Residents of the opposition-held towns of Madaya and Zabadani, which were formerly summer resorts, joined the 2011 uprising against President Bashar Assad. Residents of Foua and Kfraya, besieged by the rebels, have lived under a steady hail of rockets and mortars for years, but were supplied with food and medicine through military airdrops.
"I didn't know what was happening, all I could hear was people crying and shouting", she said.
It was unclear who carried out Saturday's bombing attack.