A suicide car bomb attack on buses carrying Syrians taken from two besieged government-held towns killed at least 100 people on Saturday.
The Syrian Observatory for Human Rights said the blast targeted buses carrying residents moved from the northern towns of Fuaa and Kafraya under a deal reached between the government and rebels.
Bodies were still being recovered at a transit point in Rashidin, west of Aleppo, according to the Observatory. More people were feared dead.
"The suicide bomber was driving a van supposedly carrying aid supplies and detonated near the buses," the Britain-based anti-government monitoring group said.
It said that most of the dead were displaced people fleeing the fighting, but also included several rebels who had been guarding the buses.
Syrian rescue workers who operate in opposition areas said at least 100 people were killed.
The Syrian Civil Defence in Aleppo province, also known as the White Helmets, said its volunteers removed 100 bodies from the scene.
Syrian state TV said the transfer resumed after the explosion, and dozens of wounded were taken to government areas.
Al Ikhbariya TV said 48 wounded were taken in exchange for allowing five buses of residents from opposition areas to head towards a rebel-controlled province.
Thousands of displaced had been stuck on the road because of a disagreement over the number of rebels allowed to leave two other towns included in the deal, but the process restarted following the blast, the Observatory said.
There were several bodies on the ground in rebel-held Rashidin.
The bombing took place as thousands of civilians from Fuaa and Kafraya waited to continue their journey to government-controlled Aleppo, the coastal province of Latakia, or Damascus.
More than 5,000 people who had lived under a crippling siege for more than two years left the two towns, along with 2,200 removed from rebel-held Madaya and Zabadani on Friday.
Meanwhile, US-backed fighters reached the outskirts of a key ISIL-held town in northern Syria on Saturday as part of an offensive aimed at Raqqa – the de facto Syrian capital of ISIL’s self-proclaimed "caliphate".
The Syrian Democratic Forces, an Arab-Kurdish alliance supported by US-led coalition air strikes and special forces advisers, surrounded Tabqa this month and have cut its main supply routes.
The town and a vast nearby dam are considered key prizes in the offensive for Raqqa, about 55 kilometres to the east.
An SDF military source said the alliance’s forces were "trying to penetrate the town from the east and west".
The alliance was reported to have advanced overnight after driving the militants from two areas south-east and south-west of the town.
SDF fighters are within a few hundred metres of Tabqa, said Observatory head Rami Abdelrahman.
The SDF launched its campaign for Raqqa in November and has since captured most of the surrounding province.
Backed by Russia and local militias, pro-government forces have made a string of recent gains.
The government and rebels have brokered deals to move people from besieged areas, which Damascus claimed was the best way to end the violence. Rebels said they were forced out by siege and bombardment.

Source: The National