Friday’s first bombing killed 53 people in the village of Sousyan, 10km northwest of Al Bab, and struck Syrian rebels battling ISIL, or the Islamic State of Iraq and the Levant group, local sources said.
The second explosion took place a few hours later and left eight dead, according to the Aleppo Media Center and Thiqa News agency, media platforms operated by activists.
The first suicide bomber targeted a checkpoint manned by Free Syrian Army (FSA) fighters that was crowded with civilians early on Friday.
The Turkish-backed rebels on Thursday drove ISIL from Al Bab, the group’s last significant stronghold in northwest Syria, along with two smaller neighbouring towns, Qabasin and al-Bezah, after weeks of street fighting.
Referring to the first bombing, the medical charity Ambulanciers Sans Frontieres said 45 people, mostly civilians, had been killed and about 70 others were wounded.
“A large number of civilians were gathering around a checkpoint and suddenly a suicide car bomber drove in and detonated,” Al Jazeera’s Andrew Simmons, reporting from Gaziantep on the Syria-Turkey border, said.
“There could be Free Syrian Army members counted in the casualty figures as well. This is really a warning shot from ISIL it would appear.”
The car bomb hit outside a security office where civilians had gathered seeking permission to return to Al Bab.
A rebel fighter with the Sultan Murad Brigade near Al Bab told Reuters news agency: “It was done on a checkpoint but there were a lot of families there gathered and waiting to get back to Al Bab. Therefore, we have many civilian casualties.
“There are still lots of cells inside Al Bab. It is very dangerous. Our search-and-clear operation is still under way.”
ISIL claimed responsibility for the first attack via social media.
On Thursday, several Turkish-backed Syrian rebels were killed by a mine in Al Bab while clearing the town of unexploded ordnance after ISIL retreated, according to reports.
Syria’s main conflict pits President Bashar al-Assad, backed by Russia, Iran and Shia militias, against rebels that include groups supported by Turkey, the US and Arab Gulf countries.
However, both those sides, as well as a group of militias led by Kurdish forces and supported by the US, are also fighting ISIL, which holds large expaneses of northern and eastern Syria.
Turkey directly intervened in Syria in August in support of a group of rebel factions fighting under the FSA banner to drive ISIL from its border.
It also wants to stop Kurdish groups from gaining control of most of the frontier.