Syria TV says at least 22 people were killed in an explosion that hit near evacuation buses in northern Syria.
The agreement had stalled, leaving thousands of people from both government-besieged and rebel-besieged areas stranded at two transit points on the city's outskirts, before the explosion occurred.
Monitoring group the Syrian Observatory for Human Rights put the death toll at 43, adding that it would likely rise because of the extensive damage.
Footage from the scene showed bodies, including those of fighters, lying alongside buses, some of which were charred and others gutted from the blast.
Ahmed Afandar, a resident evacuated from his home town near Madaya, said dozens of buses carrying women, children and men had not been allowed to proceed toward rebel-held Idlib as planned.
"They were residents of two besieged Shia minority villages, who'd been besieged by rebels for years".
Thousands of evacuees from Madaya and Zabadani were also stuck in regime-controlled Ramusa, south of Aleppo.
At the time, the USA officials said al-Hakim was believed to be linked to the 2015 attacks at the French satirical newspaper Charlie Hebdo, mentoring the brothers who gunned down the cartoonists at the French paper in 2015. They circulated a statement on social media imploring "international organizations" to intervene so the situation did not escalate.
This frame grab from video provided by the government-controlled.
The convoy of buses, which were parked at the time, was carrying thousands of people from two regime-held but rebel-besieged villages in northwestern Syria, state-run media reported.
According to Abdul Hakim Baghdadi, an interlocutor who helped the government negotiate the evacuations, 140 were killed in the attack. He said it is not clear what hinders the completion of the evacuation.
A pro-opposition activist said insurgents blamed the delay partly on the fact that a smaller number of pro-government fighters had left the Shiite villages than was agreed.
"After Aleppo I'll see what the rest of the group is doing, if there are any preparations". It said he was a militant with al-Qaida-linked groups before joining IS.
"There's no drinking water or food".
Deputy Foreign Minister Sergei Ryabkov said Friday that "the exchange of information is taking place but we are not officially sating that the validity of this document has been renewed", according to the state news agency Tass.
Syrian rescue workers who operate in opposition areas say at least 100 people were killed in a blast that ripped through a bus depot where evacuees waited to be transferred to government areas.
Syria's population is mostly Sunni.
He has been backed militarily by Russian Federation, and by Shia fighters from Iran and the Lebanese Hezbollah group in Syria's six-year-old conflict.