BySara Dorn,

Forbes Staff.

A lone gunman killed two U.S. Army soldiers and a U.S. civilian interpreter in Syria on Saturday in an attack President Donald Trump said was conducted by the Islamic State.

Trump said on Truth Social “this was an ISIS attack against the U.S.,” promising “very serious retaliation,” and adding the “President of Syria, Ahmed al-Sharaa, is extremely angry and disturbed.”

The soldiers were participating in counter-terrorism operations in Palmyra when the attack occurred, Pentagon spokesperson Sean Parnell tweeted.