President Biden struck a confidant tone earlier this month when asked whether Iran would retaliate after the U.S. and its allies bombed Yemen in response to ongoing attacks on commercial vessels in the Red Sea by Iran-backed Houthi militants. 

The January 12 exchange came during the president’s visit to Emmaus, Pennsylvania to tout what he regards as the success of his administration's economic policies. 

The president said he’d "already delivered a message to" the Islamic Republic after the Yemen bombings. 

"They know not to do anything," President Biden said, assuring that attacks on the Houthis would continue so long as they "continue this outrageous behavior." 

He declined to say whether the U.S. was in a "de facto proxy war with Iran." 

But just a little over two weeks later, three American troops were killed and dozens of others were injured in a drone strike in northeast Jordan near the Syrian border. Most, if not all, of those injured and killed were Army soldiers at a base known as Tower 22, which has been in support of the counter-ISIS mission for years, the official said.

The president as well as Secretary of Defense Lloyd J. Austin blamed Iran-backed militias for Sunday's attack. A coalition of Iran-backed militant groups calling themselves the "Islamic Resistance in Iraq" claimed responsibility. 

Later Sunday, President Biden said the U.S. "had a tough day in the Middle East," and vowed: "We shall respond." 

The troops’ death marked a major escalation of tensions in the region, after months of strikes by militia groups on American forces in the region in the wake of the Israel-Hamas war. 

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President Biden said the United States "will hold all those responsible to account at a time and in a manner (of) our choosing."

Secretary Austin said he was "outraged and deeply saddened" by the fatalities and the injuries. 

"These brave Americans and their families are in my prayers, and the entire Department of Defense mourns their loss," he said. "Iran-backed militias are responsible for these continued attacks on U.S. forces, and we will respond at a time and place of our choosing." 

He added: "The President and I will not tolerate attacks on American forces, and we will take all necessary actions to defend the United States, our troops, and our interests."

The U.S. military base at al-Tanf in Syria is just 12 miles north of Tower 22. The Jordanian installation provides a critical logistical hub for U.S. forces in Syria, including those at al-Tanf, which is near the intersection of the Iraq, Syria and Jordan borders.

Since the war in Gaza began Oct. 7, Iranian-backed militias have struck American military installations in Iraq more than 60 times and in Syria more than 90 times, with a mix of drones, rockets, mortars and ballistic missiles. 

Scores of U.S. personnel have been wounded, including some with traumatic brain injuries, during the attacks.

The militias have said that their strikes are in retaliation for Washington's support for Israel in the war in Gaza and have also said they aim to push U.S. forces out of the region.

The U.S. in recent months has struck targets in Iraq, Syria and Yemen to respond to attacks on American forces in the region and to deter Iran-backed Houthi rebels from continuing to threaten commercial shipping in the Red Sea.

Fox News’ Danielle Wallace, Liz Friden and The Associated Press contributed to this report.