President Donald Trump says “there will be very serious retaliation” after two U.S. service members and one American civilian were killed in an attack in Syria that the United States blames on the Islamic State group.

Two members of the U.S. Army and a civilian interpreter were killed, with three other Americans and two Syrians injured, in a shooting by a lone gunman Saturday in Syria.

President Trump vowed retaliation Saturday after two U.S. Army soldiers and a civilian U.S. interpreter were killed in an attack in Syria, an incident the Pentagon said occurred during “a key leader engagement.

Since the fall of Syrian dictator Bashar al-Assad last December, the Trump administration has embraced the new Syrian leader, Ahmed al-Sharaa, who has ties to Al Qaida. The Islamic State, which the U.S. declared in 2019 was mostly defeated, has remained a threat in Syria and has continued to conduct attacks since Assad’s departure.

American and Syrian military personnel were injured when an unidentified attacker opened fire on their patrol in the central Syrian town of Palmyra, Syrian state news agency SANA reported on Saturday.

Injuries were reported in an attack that the Syrian government’s news agency said happened near the ancient city of Palmyra.