At least 68 children died in a blast that hit buses carry evacuees from besieged towns in Syria, according to a monitoring group.
The death toll from the bomb attack on a crowded bus convoy outside Aleppo has reached at least 126 - including the dozens of children - in the deadliest such incident in Syria in almost a year, the Syrian Observatory for Human Rights (SOHR) said.
Syrian rescue workers of the Civil Defence said that they had taken away at least 100 bodies from the site of Saturday's blast, which hit buses carrying Shia residents as they waited to cross from rebel into government territory in an evacuation deal between the warring sides.
The British-based Observatory said the number was expected to rise.
The United Nations is not overseeing the transfer deal, which involves residents of al-Foua and Kfarya, as well as the opposition-held towns of Madaya and Zabadani. All four have been under siege for years, their fate linked through a series of reciprocal agreements that the UN says have hindered aid deliveries.
Those killed in the blast were mostly residents of the villages of al-Foua and Kefraya in Idlib province, but included rebel fighters guarding the convoy, the SOHR said.
There was no immediate claim of responsibility for the attack, which pro-Damascus media said was carried out by a suicide car bomber.
Syria's main armed opposition condemned the bombing, with groups fighting under the banner of the Free Syrian Army describing it as a “treacherous terrorist attack”.
Pope Francis, in an Easter message, also condemned the attack, describing it as “ignoble”, and asking God to bring healing and comfort to what he called the “beloved and martyred Syria”.
The convoy was carrying at least 5,000 people including civilians and several hundred pro-government fighters, who were granted safe passage out of the two Shia villages which are besieged by rebels.
Under the evacuation deal, more than 2,000 people, including rebel fighters, were granted safe passage out of Madaya, a town near Damascus besieged by government forces and their allies.
That convoy was waiting at a bus garage in a government-held area on Aleppo's outskirts, a few miles from where the attack took place. Madaya evacuees said they heard the blast.
The evacuations were continuing on Sunday, with thousands expected to be moved by early on Monday. Rami Abdurrahman, who heads the , and Hezbollah's Al-Manar TV said 3,000 people will be evacuated from al-Foua and Kfarya, while 200, the vast majority of them fighters, will be evacuated from Zabadani and Madaya.
After the blast, some 60 buses carrying 2,200 people, including 400 opposition fighters, entered areas held by rebels in the northern province of Aleppo, Mr Abdurrahman said. More than 50 buses and 20 ambulances carrying some 5,000 Foua and Kfarya residents entered the government-held city of Aleppo, Syrian state TV said, with some of them later reaching a shelter in the village of Jibreen to the south.
UN relief coordinator Stephen O'Brien said 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.”
He called on all parties to uphold their obligations under international humanitarian and human rights law, and to “facilitate safe and unimpeded access for the UN and its partners to bring life-saving help to those in need.”
Residents of Madaya and Zabadani, formerly summer resorts, joined the 2011 uprising against President Bashar Assad. Both came under government siege in the ensuing civil war. Residents of al-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.
Critics say the string of evacuations, which could see some 30,000 people moved across battle lines over the next 60 days, amounts to forced displacement along political and sectarian lines.