The US-led coalition fighting ISIS in Syria conducted air and artillery strikes against pro-regime forces in Syria on Wednesday, killing an estimated 100 pro-regime fighters, according to a coalition statement.
The coalition described its action which if confirmed could represent the largest number of pro-regime casualties inflicted by the US-led coalition as carried out in "self-defence."
Syrian state news agency SANA described the action as an "aggression" by the coalition against "popular forces" who were fighting ISIS and the US-backed Syrian Democratic Forces. The attack had left "scores of persons dead and others injured" and caused "huge damage" to the area, SANA added.
According to a coalition statement, its strikes were carried out after forces allied with Syrian President Bashar al-Assad "initiated an unprovoked attack" against a well-established Syrian Democratic Forces headquarters where coalition advisers were working with US-backed Syrian fighters.
Some 500 pro-regime troops carried out the attack using artillery, mortar fire and Russian-made tanks "in what appears to be a coordinated attack on Syrian Democratic Forces," a US military official said.
The official said that about "20 to 30 artillery and tank rounds landed within 500 meters" of the Syrian Democratic Forces headquarters before the US-backed fighters and coalition forces "targeted the aggressors with a combination of air and artillery strikes."
"We estimate more than 100 Syrian pro-regime forces were killed while engaging (Syrian Democratic Forces) and Coalition forces," the official said.
"This action was taken in self-defense," he said, adding that pro-regime forces that returned across the river had not been targeted.
The official said no coalition or US personnel had been killed or wounded in the engagement but that one member of the Syrian Democratic Forces was wounded.
The coalition said the attack took place in Khusham in the Middle Euphrates River Valley, five miles east of the agreed-on "de-confliction" line designed to separate Russian-backed regime troops and US-backed forces in Syria.
He said the coalition suspected that pro-regime forces were attempting to seize territory, including lucrative oil fields, that the Syrian Democratic Forces had liberated from ISIS in September.
They "were likely seeking to seize oilfields in Khusham that had been a major source of revenue for Daesh from 2014 to 2017," the official said, using the Arabic acronym for ISIS.