“We call on the parties to ensure the safety and security of those waiting to be evacuated,” UN spokesman Stephane Dujarric said in a statement late on Saturday, UN News Center reported.
He added that the evacuations were being conducted in accordance with the agreement reached pursuant to the “Four Towns” Agreement, covering Foua, Kefraya, Madaya and Zabadani.
These four locations were referred to specifically in the Agreement to facilitate humanitarian access to the people in need.
In the statement, Dujarric also expressed condolences to the families of the victims of the incident and wished a speedy recovery to those injured.
Thousands of residents of the predominantly Shiite towns of Foua and Kefraya were evacuated on Friday under an exchange deal. They have been stranded at Ramouseh area on the outskirts of Aleppo, waiting for the buses carrying militants and civilians from Zabadani and Madaya to be transferred to the town of Jarabulus.
On Saturday evening, a bomber blew up an explosive-laden car near the convoy, killing nearly 40 people, mostly children.
Horror footage shows the buses engulfed in flames as people scream amid gunshots in the background.
Foua and Kefraya in the northwestern province of Idlib are encircled by Takfiri terrorists. The militant-held towns of Zabadani and Madaya near the Lebanese border are under siege by Syrian government forces.
Foua and Kefraya are the only government-held enclave in Idlib’s militant-held area.
The towns of some 20,000 people have been under siege since 2013. The humanitarian situation remains dire, with a lack of food and basic necessities.