BEIRUT/United Nations - An Islamic State car bomb killed more than 50 people on Friday in a Syrian village held by rebels, a war monitor said, a day after the militant 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 monitor of the war based in Britain, said more than 50 people died including over 30 civilians. Two rebels contacted by Reuters put the total death toll at 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 Turkey-backed rebels drove Islamic State from the town of al-Bab on Thursday, following weeks of street battles near 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.

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.

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

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 United States and Gulf monarchies.

Meanwhile, Russia said Friday it will use its veto to block a proposed UN resolution drafted by the United States, France and Britain that would impose sanctions on Syria for the use of chemical weapons.

“I just explained our position very clearly to our partners. If it is tabled we will veto it,” Russian Deputy Ambassador Vladimir Safronkov told reporters following a closed-door meeting of the Security Council.

The United States, France and Britain are pushing for a vote early next week on the proposed resolution that would slap sanctions on Syrians deemed responsible for chemical attacks in the nearly six-year war.

Safronkov rejected the measure as “one-sided,” saying it was based on “insufficient proof” and contradicted “the fundamental principle of presumption of innocence until the investigation is over.”

Russia has used its veto six times to shield its Damascus ally from any punitive action by the Security Council.

The draft resolution follows a UN-led investigation which concluded in October that the Syrian military had carried out at least three chlorine attacks on opposition-held villages in 2014 and 2015.

The joint panel of the United Nations and the Organization for the Prohibition of Chemical Weapons (OPCW) also found that Islamic State militants had used mustard gas in an attack in 2015.

US Ambassador Nikki Haley said she was not swayed by the Russian arguments.

“How much longer is Russia going to continue to babysit and make excuses for the Syrian regime?” she said.

“People have died by being suffocated to death. That’s barbaric.”

“You are either for chemical weapons or you are against it,” she added.

The draft resolution, seen by AFP, would impose a global travel ban and assets freeze on 11 Syrians, mostly military officials, and 10 entities linked to chemical weapons development.

It would also ban the sale, supply or transfer of helicopters and related materiel, including spare parts, to the Syrian armed forces or the government.

The UN-OPCW panel found that Syrian air force helicopters dropped chlorine barrel-bombs on the villages of Qmenas, Talmenes and Sarmin in 2014 and 2015.

Chlorine use as a weapon is banned under the Chemical Weapons Convention, which Syria joined in 2013 under pressure from Russia.

The Syrian government has repeatedly denied using chemical weapons in the war that has killed 310,000 people since March 2011.