The bomber blew up a vehicle packed with explosives in Susian, eight kilometers northeast of the strategic town that the Turkish-backed rebels overran.

An ISIS car bomb killed more than 50 people on Friday in a Syrian village held by rebels, a war monitor said, a day after the extremist group was driven from its last stronghold in the area.

The blast in the village of Sousian hit a security checkpoint controlled by rebels fighting under the Free Syrian Army (FSA) banner.

The Syrian Observatory for Human Rights, a monitoring organization based in Britain, said more than 50 people died including over 30 civilians. Two rebels contacted by Reuters put the total death toll at least 40.

One of the two, a fighter with the Sultan Murad Brigade near al-Bab, said: “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.”

The Turkish-backed rebels drove ISIS from the town of al-Bab on Thursday, following weeks of street battles near an area where Ankara wants to establish a safe zone for civilians.

Turkey’s military said on Friday that Syrian rebels had taken full control of all of al-Bab, and that work to clear mines and unexploded ordnance was under way.

“With al-Bab under control, the planned targets … have been achieved. In the aftermath, support will be provided to normalize life and for the local people to quickly return to their homes,” said Turkish military chief of staff Hulusi Akar.

Sousian is behind rebel lines about 8 km (5 miles) northwest of al-Bab, around which Ankara has long supported the formation of a security zone it says would help to stem a wave of migration via Turkey into Europe.

A second blast took place 2 km south of Sousian later on Friday, but it was unclear whether it was from a vehicle bomb or a planted device such as a mine. There were reports of casualties but no immediate details, the Observatory said.

ISIS said in a social media posting that it was behind the Sousian attack, having acknowledged on Thursday it had lost control of al-Bab.