An vehicle bomb has hit a convoy of buses carrying civilians evacuated from besieged towns in Syria, killing at least 16 people.
An explosion hit a bus convoy carrying evacuees near the Syrian city of Aleppo.
A British-based Syrian Observatory Human Rights group said that the Syrian government and rebels differed in last minute and the negotiation ended.
Syrian state TV says a auto bomb has exploded near buses carrying Syrians evacuated from towns besieged by rebels in northern Syria.
Residents from Kefraya and Foua were to be transferred government-controlled Jibrin, while those from Madaya and Zabadani were heading towards the rebel-held Idlib province.
They are involved in a population transfer deal but have been stranded since the agreement stalled.
The residents, alongside hundreds of pro-government fighters, had left the two rebel-besieged villages in northwest Idlib province under a deal where in exchange, hundreds of Sunni insurgents and their families moved out of a government-besieged area near Damascus.
Late Friday, the buses from Madaya arrived in Rashidin, where the evacuees from Fuaa and Kefraya were waiting, according to a resident aboard one of the buses. More than 20,000 people were bused out of Aleppo at the end of a year ago, to rebel-held provinces in the northwest.
The explosion hit an area where busses carrying almost 5,000 people from Foua and Kfraya, villages in northern Syria that have been besieged by militants.
"The people are restless and the situation is disastrous", said Mr Afandar.
The deal to evacuate government-held Fuaa and Kafraya, and rebel-held Madaya and Zabadani, is the latest such agreement in Syria's six-year civil war.
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.
Meanwhile, an Iraqi military statement said the Syrian air force has carried out a series of air strikes against so-called "Islamic State" (IS) militants inside Syria, with one killing a leading member of the group in Raqqa, the IS de facto capital.
Madaya and Al-Zadabani, both of which are located some 40 kilometers northwest of Damascus, are now encircled by regime forces, while Kefraya and Al-Fuaa - both in Syria's northwestern Idlib province - remain encircled by opposition forces.
A resident of Zabadani, Amer Burhan, said no evacuation had taken place.
Opposition officials have accused the Syrian government and its Iranian allies of using siege tactics to force demographic changes across the country, mostly along sectarian lines. Assad is from the Alawite religious minority, often considered an offshoot of Shia Islam.
He has been backed militarily by Russian Federation, and by Shi'ite fighters from Iran and the Lebanese Hezbollah group in Syria's six-year-old conflict.