Syrian pro-regime fighters initiated an unprovoked attack against Syrian Democratic Forces headquarters, where coalition service members were co-located, Wednesday, according to military officials.

Syrian Democratic Forces, the U.S.-backed mix of Kurdish and Arab fighters, acted in self-defense to repel the attack in eastern Syria late Wednesday and early Thursday, Col. Thomas Veale, a spokesman for the Inherent Resolve coalition, told Military Times.

The assault appeared “to be a coordinated attack on Syrian Democratic Forces approximately 8 kilometers east of the Euphrates River de-confliction line in Khusham, Syria,” Veale said.

Forces loyal to Syrian President Bashar al-Assad’s regime began the attack with 122mm artillery pieces, according to Veale. The pro-regime forces maneuvered T-55 and T-72 main battle tanks with support from multiple-launch rocket systems and mortars against the SDF forces headquarters, he said.

An approximately battalion-sized dismounted formation followed the tanks, he added.

“After 20 to 30 artillery and tank rounds landed within 500 meters of the SDF headquarters location, [SDF] supported by the Coalition targeted the aggressors with a combination of air and artillery strikes,” Veale said.

A rebel fighter fires a heavy machine gun during clashes with government forces and pro-regime shabiha militiamen in the outskirts of Syria's northwestern Idlib province in 2015. (Omar Haj Kadour/AFP/Getty Images)
A rebel fighter fires a heavy machine gun during clashes with government forces and pro-regime shabiha militiamen in the outskirts of Syria's northwestern Idlib province in 2015. (Omar Haj Kadour/AFP/Getty Images)

Because coalition advisers were with the SDF in an advise, assist and accompany capacity, “this action was taken in self-defense,” he added.

Additionally, fleeing pro-regime vehicles and personnel who headed back west were not targeted, according to Veale.

The coalition had been aware of a massing of pro-regime forces over the past week.

“Coalition officials alerted Russian officials of the SDF presence in Khusham via the de-confliction line well in advance of the [pro-regime] attack,” Veale explained. That line of communication was maintained with their “Russian counterparts before, during and after the thwarted [pro-regime] attack.”

Russian officials assured Inherent Resolve they would not engage coalition forces in the vicinity, Veale added.

One SDF soldier was wounded during the assualt, but there were no coalition casualties, he said, adding that there also was no number of casualties on the pro-regime side he could report at this time.

“We suspect Syrian pro-regime forces were attempting to seize terrain SDF had liberated from Daesh in September 2017,” Veale said. “[Pro-regime forces] were likely seeking to seize oil fields in Khusham that had been a major source of revenue for Daesh from 2014 to 2017.”

Members of the Syrian pro-regime forces ride atop a tank prior to advancing towards rebel-held positions west of Aleppo in November 2017. (George Ourfalian/AFP/Getty Images)
Members of the Syrian pro-regime forces ride atop a tank prior to advancing towards rebel-held positions west of Aleppo in November 2017. (George Ourfalian/AFP/Getty Images)

Veale wouldn’t break down the aircraft nationality or platform used to conduct the strike, and couldn’t disclose the number of coalition advisers on the ground during the assault.

“We also cannot speculate on the exact makeup of the Syrian pro-regime forces who conducted the attack at this time,” he added.

In addition to the Syrian army loyal to Assad, pro-regime forces are supported by Iranian-backed militias and Russian forces.

“In defense of Coalition and partner forces, the Coalition conducted strikes against attacking forces to repel the act of aggression against partners engaged in the Global Coalition’s defeat-Daesh mission,” a statement from U.S. Central Command said, using the Arabic acronym for the Islamic State (ISIS).

This is not the first clash between coalition and pro-regime forces in the Syrian civil war.

One other incident occurred last June, when a U.S. Navy F/A-18 Super Hornet shot down a Syrian regime Su-22 jet that had attacked U.S.-backed forces on the ground.

“The Coalition remains committed to focusing on the defeat-Daesh mission in the Middle Euphrates River Valley and asserts its non-negotiable right to act in self-defense,” the CENTCOM statement added.