Yesterday's blast hit a convoy carrying residents from the northern towns of Fuaa and Kafraya as they waited at a transit point in rebel-held Rashidin, west of Aleppo.
At least 68 children were among those killed in the attack, the Syrian Observatory for Human Rights said, updating a previous toll of 112 dead.
At least 109 of the dead were evacuees, the Britain-based monitoring group said, while the rest were aid workers and rebels guarding the convoy.
The agreement is the latest in a string of evacuation deals, which the government of President Bashar al-Assad says are the best way to end the violence after more than six years of civil war.
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Rebels say they amount to forced relocations after years of bombardment and crippling sieges.
Body parts and the belongings of evacuees - including clothes, dishes and even televisions - were still strewn at the scene of the attack today, an AFP correspondent said.
There was no immediate claim of responsibility for the bombing, though the key Ahrar al-Sham rebel group denied any involvement. The government blamed "terrorists" - a catch-all term for its opponents.
The Observatory, which relies on a network of sources inside Syria to monitor the conflict, said hundreds of people were also wounded in the blast.
It said a petrol station at the transit point was caught up in the explosion, adding to the number of victims.
Maysa al-Aswad, a 30-year-old evacuee from Kafraya, said she was sitting on one of the buses with her six-month-old son Hadi and 10-year-old daughter Narjis when the blast shook the parked convoy.
"Hadi was on my lap and Narjis on a chair next to me. When the explosion happened I hugged them both and we fell to the floor," she told AFP by telephone from near Aleppo.
"I didn't know what was happening, all I could hear was people crying and shouting," she said.
"All I can think about is how we survived all the death during the last few years and then could have died just after we finally escaped."
The evacuation process resumed after the bombing, the Observatory said, with the residents of Fuaa and Kafraya eventually arriving in Aleppo, Syria's second city which the government gained full control of last year.
Wounded survivors, including many children, were taken for treatment at an Aleppo hospital.