Roughly 200 U.S. troops were evacuated by C-130 transport planes prior to the attack last week, while about two dozen remained at the small base, one military official told Fox News. While it was not clear what type of intelligence led to the tip, multiple officials say it saved lives.
No American troops were injured or killed in the attack on the base, located near the borders of Iraq and Jordan, but bomb fragments were later discovered in areas where troops sleep and stand guard.
U.S. officials believe Iran authorized and resourced the attack using proxy forces, though officials do not believe the attack, which sent five drones to target the base housing hundreds of U.S. forces, originated in Iran.
U.S. forces are based at the al-Tanf garrison, which is also on a road that serves as a vital link from Tehran to Iranian-backed forces that train Syrian forces to combat Islamic State militants.
At a press conference Monday, Pentagon spokesman John Kirby called the attack "complex, coordinated and deliberate," noting that similar attacks have in the past originated from Shia militia groups tied to Iran.
Kirby also declined to offer details on how the U.S. could respond to the attack.
"The protection and security of our troops overseas remains a paramount concern for the secretary," Kirby said, referring to Defense Secretary Lloyd Austin. "If there is to be a response, it will be at a time and a place and a manner of our choosing, and we certainly won't get ahead of those kinds of decisions."
About 900 U.S. troops remain in Syria to assist efforts to combat the Islamic State. There are thousands of ISIS prisoners there, including fighters and family members still in Syria, guarded by U.S.-backed Kurdish forces. Some fear if U.S. troops leave, those fighters will get out.