The Pentagon said the U.S. military launched numerous air strikes in Syria on Thursday night against Iran-aligned forces it blamed for a drone assault that killed an American contractor, injured another, and wounded five troops earlier in the day.

The Pentagon announced the attack on U.S. personnel and retaliation late Thursday.

It said the attack against U.S. personnel took place at a coalition base near Hasakah in northeast Syria at approximately 1:38 p.m. (1038 GMT) on Thursday.

The U.S. intelligence community concluded that the one-way attack drone was Iranian in origin, the military said, a decision that may further worsen already strained ties between Washington and Tehran.

President Joe Biden ordered the retaliatory strikes, which targeted Iranian Revolutionary Guard Corps facilities, according to U.S. Defense Secretary Lloyd Austin (IRGC).

“Today’s incident and a series of previous attacks on Coalition forces in Syria by terrorists linked with the IRGC prompted the air strikes,” Austin said.

“No faction will strike our forces with impunity.”

After the drone attack, the military said three service members and a contractor needed medical evacuation to Iraq, where the U.S.-led coalition fighting Islamic State has medical facilities.

The Pentagon said two more wounded American troops were treated at the northeast Syria base.

Even though drone strikes against U.S. soldiers in Syria are routine, one dead and six wounded are exceptional.

Army General Erik Kurilla heads Central Command and says Iranian-backed groups have attacked U.S. troops 78 times since 2021.

On Thursday, Kurilla warned the House Armed Services Committee about Iran’s drone fleet.

“The Iranian regime now holds the largest and most capable unmanned aerial vehicle force in the region,” he said.

Three drones targeted a U.S. base in January in Syria’s Al-Tanf region. The U.S. military shot down two drones, and the third hit the compound, injuring two Syrian Free Army forces.

U.S. authorities suspect Iran-backed militia are directing drone and rocket assaults, highlighting Syria’s complicated geopolitics, where Syrian President Bashar al-Assad relies on Iran and Russia and views U.S. soldiers as invaders.

The attack occurred just weeks after the top U.S. general, Mark Milley, visited northeast Syria to assess the mission against Islamic State and the risk to U.S. personnel.

Milley told reporters traveling with him, “If you think that that’s important, then the answer is ‘Yes.'”

Milley added, “That’s important.”

Although Islamic State is a shadow of the group that ruled over a third of Syria and Iraq in a Caliphate declared in 2014, hundreds of fighters are still camped in desolate areas where neither the U.S.-led coalition nor the Syrian army, with support from Russia and Iranian-backed militias, have full control.

Kurdish-led Syrian Democratic Forces, America’s key ally in Syria, detain thousands of Islamic State fighters.

U.S. authorities warn Islamic State might yet become a big danger.

Former President Donald Trump nearly ended the operation in 2018 before relaxing his exit plans. It is a relic of the bigger global battle against terrorism that encompassed the war in Afghanistan and a far larger U.S. military commitment to Iraq.