Two Syrian security personnel, two U.S. service members, and one U.S. civilian were killed Saturday in an attack on a joint Syrian-U.S. patrol near the ancient city of Palmyra, Syrian authorities and the U.S. Central Command reported.

The attack occurred during a joint field tour involving Syrian internal security leadership and the joint forces near Palmyra in Syria's central Homs province, amid prior warnings issued by Syrian security authorities about potential threats from the Islamic State (IS) group in the desert region, Interior Ministry spokesman Noureddin al-Baba told state television al-Ikhbariya.

The attacker was a gunman affiliated with the Internal Security Command in the Syrian desert region and had previously been flagged in an internal security assessment for suspected extremist views, al-Baba said. Disciplinary measures were scheduled for Sunday, the first official working day of the week, but the attack occurred before the planned action could be taken, he added.

He said the attacker, who was killed during the exchange of fire, held no leadership role in the security forces and was not assigned to escort senior officials.

Investigations are ongoing to determine whether the assailant had direct organizational links to IS.

The incident prompted heightened security measures, including the temporary closure of the Deir al-Zour-Damascus highway, as authorities reiterated their commitment to strengthening internal oversight and preventing security breaches.