The death toll in a suicide car bomb attack on buses carrying Syrians evacuated from two besieged government-held towns has risen to at least 112, a monitoring group said today.

The Syrian Observatory for Human Rights said that 98 evacuees from the northern towns of Fuaa and Kafraya were killed when an explosives-laden vehicle hit their buses at a transit point west of Aleppo yesterday.

It said the remainder of the dead were aid workers and rebels tasked with guarding the buses.

It warned the death toll may rise further as "hundreds" more were wounded in the blast.

Dozens of buses carrying several thousand refugees had been stuck by the roadside in the rebel-held town of Rashidin after leaving Fuaa and Kafraya on Friday under a deal reached between the government and opposition groups.

Fuaa and Kafraya have been under rebel siege for more than two years. As part of the deal, several hundred people including armed rebels will be transported out of Madaya and Zabadani, towns near Damascus, which are surrounded by pro- government forces.

Syria's six-year civil war has seen several similar deals, which the government of President Bashar al-Assad says are the best way to end the violence. Rebels say they are being forced to relocate through bombardment and seige.

The government blamed yesterday's attack on "terrorists" -- its catch-all term for opposition groups.

The influential rebel Ahrar al-Sham force denied involvement, with a senior official tweeting: "Our role was to secure civilians not kill them."

The blast puts the four-town evacuation deal, brokered partly by rebel backer Qatar and government ally Iran, in doubt.

The Observatory said after the bombing that the evacuation process had resumed, but it was not immediately clear today if convoys had restarted their journeys.