An Islamic State flag is pictured above a destroyed house near the Clock Square in Raqqa, Syria, Oct. 18, 2017. Photo: Reuters / Erik De Castro.

An airstrike, probably carried out by US-led international forces or Iraq, struck an Islamic State-held area of eastern Syria, killing 54 people including 28 civilians as well as members of the jihadist group, a war monitor said on Friday.

The Syrian Observatory for Human Rights said the airstrike hit the area near the towns of al-Sousa and al-Baghouz Fawkani on Thursday.

Colonel Sean Ryan, a spokesman for the US-led coalition, said that it or “partner forces may have conducted strikes in the vicinity.” The coalition would assess the report alleging civilian casualties, he added, in an emailed response to a question from Reuters.

“We have no further information at this time,” he added.

The US-led coalition is fighting to crush the remnants of Islamic State on both sides of the border between Syria and Iraq. In Syria it operates in support of the Syrian Democratic Forces (SDF), an alliance of militias that includes Kurds.

The Observatory said the attack had targeted an ice factory east of Sousa a few kilometers (miles) from the border with Iraq. Most of the civilians killed were Iraqis.

The death toll could rise because of dozens more people had been wounded including some in critical condition, the Observatory said.

Earlier reports by the Syrian state news agency SANA and the pro-Damascus al-Watan newspaper accused the US-led coalition of carrying out the airstrike. Reuters could not independently verify those reports.

Islamic State was largely defeated in most of the territory it controlled in both countries last year, but fighters still operate in the desert near the border.