EXCLUSIVE: The U.S. military was tipped off prior to an Iran-backed drone attack on a base in Syria housing American forces.

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.

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NORTHEASTERN SYRIA - MAY 25:  U.S. Army soldiers prepare to go out on patrol from a remote combat outpost on May 25, 2021 in northeastern Syria. U.S. forces, part of Task Force WARCLUB operate from combat outposts in the area, coordinating with the Kurdish-led Syrian Democratic Forces (SDF) in combatting residual ISIS extremists and deterring pro-Iranian militia.  (Photo by John Moore/Getty Images) (John Moore/Getty Images)

US TROOPS IN SYRIA TARGETED WITH 'DELIBERATE AND COORDINATED' DRONE ATTACK, NO INJURIES REPORTED

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.

In this picture released on Aug. 5, 2015 by the Rased News Network, a Facebook page affiliated with ISIS, an ISIS militant stands on a tank captured from Syrian government forces, in the town of Qaryatain southwest of Palmyra, central Syria.

An ISIS militant stands on a tank captured from Syrian government forces, in the town of Qaryatain southwest of Palmyra, central Syria. (Photo released Aug. 5, 2015 by Rased News Network, a Facebook page affiliated with ISIS/via AP)

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.

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Kirby also declined to offer details on how the U.S. could respond to the attack.

Pentagon spokesman John Kirby speaks during a briefing at the Pentagon in Washington, Thursday, Aug. 12, 2021. With security rapidly deteriorating in Afghanistan, the United States is evacuating some personnel from the U.S. Embassy in Kabul, and U.S. troops with be assisting at the Kabul airport. (AP Photo/Andrew Harnik)

"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.