BEIRUT // An air strike by US-led forces in Syria has killed 52 people, including seven children, in the northern province of Aleppo.

The death toll from Friday’s strike was the highest civilian loss in a single attack by US and Arab forces since they launched air strikes against extremist groups in Syria, a Britain-based monitoring group said on Saturday.

The raid mistakenly struck civilians in a village on the eastern banks of the Euphrates River, killing members of at least six families, the Syrian Observatory for Human Rights said.

US-led strikes had killed at least 66 civilians in Syria from the start of the raids on September 23 until Friday’s strike, which brought the total to at least 118. The campaign has also killed nearly 2,000 ISIL fighters.

The Observatory said at least 13 people were still missing from Friday’s raid.

The United States has said it takes reports of civilian casualties from the strikes seriously and investigates each allegation.

The US-led air campaign has had little impact on ISIL, slowing its advances but failing to weaken the group in areas it controls. The group has built its own government in the Syrian city of Raqqa, where it is most powerful.

Washington and its allies say their aim is to support what they call moderate rebels fighting against both Syrian president Bashar Al Assad and ISIL.

The latest US-led plan to train and arm a Syrian opposition force will begin in Turkey on May 9, Ankara’s foreign minister Mevlut Cavusoglu told a Turkish newspaper on Friday.

But the programme to train and arm a force that is expected to eventually total more than 15,000 troops has been mired in delays as many details of the plan, such as whether or how Washington would come to their aid on the battlefield, remain unclear.

Syrian government forces have seen a series of setbacks on the battlefield recently and hardline fighters have edged closer to the president’s stronghold in the coastal areas.

Fighting continued on Saturday between government forces and militants in government-held Latakia, the heartland of Mr Al Assad’s minority Alawite community.

The violence follows advances in neighbouring Idlib province by the hardline Ahrar Al Sham group and Syria’s Al Qaeda affiliate, Jabhat Al Nusra, as well as other allied fighters.

Syria’s state news agency said the army carried out overnight strikes on Al Nusra positions in Idlib.

Meanwhile, state media said that at least 12 civilians had been killed in rebel shelling in government-held districts of Aleppo city on Saturday, including three children.

The shelling killed eight members of the same family and also left 45 people injured, Syrian state TV said. The country’s state news agency, quoting an unnamed police official, said three children were among those killed. The official said the shells hit a residential area, damaging homes, shops and cars.

The Observatory, which relies on a network of activists inside the country, said rebel attacks in government-controlled areas had killed at least five people, including one in an overnight attack. However, it said the death toll was likely to rise because many of the injured were in critical condition.

The discrepancy in casualty estimates couldn’t be immediately reconciled but such differences are not uncommon in the immediate aftermath of attacks.

* Reuters and Associated Press