The death toll from an air strike in eastern Syria has risen to 54 overnight, including ISIS fighters and 28 civilians, a war monitor said on Friday.
The raid in one of the last holdouts of ISIS in Deir Ezzor province hit a "gathering of civilians" at an ice factory near the village of Al Soussa near the Iraqi border, the Britain-based Syrian Observatory for Human Rights said.
Most of the civilians were Iraqi, Observatory Director Rami Abdulrahman said.
He said the air strike had most likely been carried out either by the US-led coalition against ISIS or Iraqi forces that are working with it.
Iraqi jets have recently carried out strikes in eastern Syria, while coalition aircraft have been supporting Kurdish-led fighters battling the extremists.
The Syrian state news agency Sana and the pro-Damascus Al Watan newspaper said the coalition carried out the air strike near the town of Albu Kamal east of the Euphrates River.
The coalition was not immediately available for comment.
ISIS fighters swept across Syria and Iraq in 2014, declaring a cross-border "caliphate" in areas they controlled.
They have since lost most of that territory to various offensives, but still retain pockets in Syria including in Deir Ezzor.
Al Soussa lies to the east of the Euphrates River, which runs diagonally through Deir Ezzor, splitting the province in half.
Russia-backed regime forces have pushed back the extremists on the western side of the Euphrates, while the US-backed Syrian Democratic Forces alliance have battled them to its east.
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An air strike in the area in June killed more than 50 pro-regime fighters, most of them from Iraqi militia backed by Iran, an ally of the Syrian regime.
The US-led coalition was initially blamed for the attack but US officials later said it had been carried out by Israel, which has carried out several raids on Iran-linked targets in Syria.
The Observatory said at least 30 Iraqi fighters were killed in the strike near the town of Albu Kamal on the Syria Iraq border.