A Syrian bus convoy transporting the residents of two villages being evacuated in a deal between warring parties has been hit by a blast on the outskirts of Aleppo. The UN condemned the attack and has demanded that all parties offer safe passage to evacuees.

The blast was reportedly caused by a suicide attacker detonating a car bomb. While Syrian state media said at least 39 were killed, sources on the ground told Xinhua that at least 70 people died and 128 others injured in the bomb attack. That number was confirmed by another source to RIA.

Pictures have emerged on social media purporting to show the aftermath of the blast.

عشرات القتلى والجرحى جراء تفجير قرب تجمع للخارجين من كفريا والفوعة في منطقة الراشدين غرب حلب#حلب_اليوم#سورية#سورياpic.twitter.com/YIl4Fgws8X — HalabToday حلب اليوم (@HalabTodayTV) April 15, 2017

Humanitarian workers were among the victims of the attack, according to Arabic Asharq Al-Awsat.

Very graphic footage from the scene posted online shows burned out vehicles with the dead lying on the ground and inside buses, some covered with blankets.

“A very powerful blast” killed “many women and children” inside the buses, an eyewitness said while filming the video. There were also fighters from the Free Syrian Army and other groups who were securing the area among the victims, he added.

صور من المفخخة التي ضربت تجمعا لمسلحي واهالي كفريا والفوعة عند مدخل حلب pic.twitter.com/50FYNRPFeZ — ابو الهدى الحمصي (@aboalhodaalhoms) April 15, 2017

Photos from the scene show bodies near blackened buses with blown out windows.

The bus convoy was transporting up to 5,000 residents from the mostly Shiite villages of al-Foua’a and Kefraya.

Terrorists reportedly loaded the car in which they hid the bomb with children’s food supplies to sneak it into the area, SANA reported, citing its correspondent.

At least three members of Syrian Arab Red Crescent (SARC) were moderately injured in the attack, while a few of the humanitarian organization’s ambulances were damaged in the blast, according to a source within SARC quoted by SANA.

The staff were supervising the evacuation process.

Several hours after the attack, the transfer resumed, AP reported, citing Syrian television.

The attack took place on the outskirts of Aleppo in the Rashideen area while the convoy was waiting to enter the city.

The buses were waiting to take people who were evacuated from the two Shiite villages on Friday from rebel-held territory into the government-controlled city.

So-called rebels bomb government civilian evacuees near Aleppo: is Britain on this murderous side of the argument in Syria? pic.twitter.com/l1DYy78I7A — Russian Embassy, UK (@RussianEmbassy) April 15, 2017

The residents, along with hundreds of pro-government fighters, had come from the two rebel-besieged villages in northwest Idlib province, Reuters reported. In exchange, hundreds of Sunni insurgents and their families moved out of government-controlled areas near Damascus, Syria’s capital.

However, a delay in the agreement has reportedly left thousands of evacuated people stranded at two transit points on Aleppo’s outskirts since late Friday.

The United Nations Saturday condemned the blast saying those responsible must be brought to justice.

"We condemn the attack today in Rashideen, west Aleppo, on 5,000 evacuees traveling from the towns of Foah and Kefraya to government-controlled areas," Stephane Dujarric, spokesperson for UN Secretary-General Antonio Guterres, said in a statement.

"We call on the parties to ensure the safety and security of those waiting to be evacuated," he said, adding that "those responsible for today's attack must be brought to justice."

The United States also condemned the blast targeting calling it a “barbaric” attack against innocent civilians.

"We deplore any act that sustains and empowers extremists on all sides including today's attacks, as well as forced migration, increased displacement, and all forms of violence directed against civilians in Syria," State Department spokesman Mark Toner said in a statement.