Hundreds of frightened Syrians being evacuated from besieged towns were stuck Thursday at a rebel-held transit point where dozens of their fellow townspeople were killed in a weekend bombing.
The 3,000 evacuees left their homes in the government-controlled towns of Fuaa and Kafraya at dawn on Wednesday as part of a deal that is also seeing residents and fighters transported out of several rebel areas surrounded by government forces.
The evacuations began last week but were delayed after Saturday's suicide car bombing, which saw 126 people killed, 68 of them children, at the transit point in Rashidin, west of Aleppo.
They resumed on Wednesday but evacuees were forced to spend the night in buses at the marshalling area following another delay.
The Syrian Observatory for Human Rights said the latest delay was the result of an 11th-hour rebel demand for the release of prisoners held by President Bashar al-Assad's government.
"The convoys will not move until after the release of 750 prisoners -- men and women -- from regime prisons and their arrival in rebel-held areas," the British-based monitoring group said.
On Thursday, an AFP correspondent saw the evacuees gathered together at the transit point, surrounded by armed rebels, as children played near the waiting buses.
Umm Sanad, a 50-year-old woman from Fuaa, said they had overcome their fear to join the evacuation.
"We left because of the siege and the rockets. We left even though we were afraid after the attack," said Sanad, who evacuated along her sons aged 15 and 17.
The rebel fighters were keeping all other cars away from the area, except for a Red Crescent vehicle that was allowed to distribute aid.
Saturday's attack was one of the deadliest since the start of Syria's six-year civil war and was widely condemned for targeting civilians.
The United Nations said Thursday that whoever was behind the bombing had been pretending to provide aid and may have targeted children.
"Someone pretending even to distribute aid and attracting the children produced that horrific explosion," UN Syria envoy Staffan de Mistura told reporters in Geneva.
No group has claimed responsibility for the bombing. The government blamed "terrorists" -- a catch-all term for its opponents.
The current evacuations mark the end of the first stage of a deal brokered by regime ally Iran and Qatar, a longtime supporter of Syrian rebel groups.
Shiite-dominated Iran has repeatedly raised concerns for the mainly Shiite residents of Fuaa and Kafraya, who are besieged by Sunni rebels and Islamists who control the surrounding Idlib province.
Under the agreement, residents and rebel fighters are being evacuated from the towns of Madaya, Zabadani, and other nearby oppositions-held areas close to Damascus.
On Wednesday, 11 buses carrying around 300 people left Zabadani and two other rebel-held areas around Damascus.
They were being held up on Thursday at a staging point at Ramussa in government-held territory, the Observatory said.
When the current phase of evacuations is complete, a total of 8,000 people should have left Fuaa and Kafraya in exchange for 2,500 civilians and rebels from opposition areas.
A second phase of the evacuations -- which in all will see up to 30,000 people transferred from their homes -- is to begin in June.
Assad's regime has presented evacuation deals as the best way to end Syria's war, which has killed more than 320,000 people and forced more than half the population from their homes.
The opposition says the evacuations amount to forced relocation after years of bombardment and siege.
Syria's opposition and Western leaders have accused Assad's regime of a wide range of abuses during the conflict, including a suspected chemical attack on the rebel-held town of Khan Sheikhun earlier this month that killed at least 87 people.
The head of a global arms watchdog said Wednesday that "incontrovertible" test results showed that victims in Khan Sheikhun had been exposed to sarin gas or a similar substance.
Samples from 10 victims of the April 4 attack analysed at four laboratories "indicate exposure to sarin or a sarin-like substance," said Ahmet Uzumcu, head of the Organisation for the Prohibition of Chemical Weapons.
A few days after the incident, US forces carried out a missile strike on a Syrian airbase from where Washington claimed the chemical attack was launched, in the first direct American action against Assad's regime.