WASHINGTON - The Pentagon said the US military carried out multiple air strikes in Syria on Thursday night against Iran-aligned groups it blamed for a deadly drone attack that killed an American contractor, injured another, and wounded five US troops earlier in the day.

Both the attack on US personnel and the retaliation were announced by the Pentagon late Thursday.

The attack on US personnel occurred on Thursday around 1:38 p.m. (1038 GMT) at a coalition base near Hasakah in northeast Syria.

According to the military, the one-way attack drone was Iranian in origin, according to the U.S. intelligence community. This assessment could exacerbate already tense relations between Washington and Tehran.

President Joe Biden ordered the retaliatory strikes, according to U.S. Defense Secretary Lloyd Austin, which targeted locations used by organizations connected to Iran's Islamic Revolutionary Guard Corps (IRGC).

The airstrikes were carried out in retaliation for today's attack as well as a string of recent assaults on Coalition forces in Syria by organizations linked to the IRGC, according to Austin's statement.

No one or anything will be allowed to attack our troops.

According to the military, three service members and a contractor who suffered injuries as a result of the drone attack had to be medically evacuated to Iraq, where the U.S.-led coalition fighting the remaining members of the Islamic State has medical facilities.

The Pentagon reported that the other two injured American soldiers were treated at the base in northeast Syria.

Despite the fact that drone attacks against American personnel in Syria are attempted frequently, the number of casualties — one fatality and six injuries — is extremely unusual.

Army General Erik Kurilla, who is in charge of U.S. troops in the Middle East as the head of Central Command, estimates that Iranian-backed groups have attacked American forces about 78 times since the start of 2021.

Kurilla issued a warning about Iran's drone fleet during his earlier testimony on Thursday before the House Armed Services Committee.

The largest and most effective unmanned aerial vehicle force in the area is currently held by the Iranian regime, he claimed.

In the Al-Tanf region of Syria in January, three drones targeted a U.S. base. According to the US military, two of the drones were shot down, and the third one crashed into the compound, injuring two Syrian Free Army soldiers.

As a reminder of the intricate geopolitics of Syria, where Syrian President Bashar al-Assad relies on the support of Russia and Iran and sees American troops as occupiers, U.S. officials believe that militias supported by Iran are behind the drone and rocket attacks.

The assault occurred only a few weeks after Mark Milley, the top American general, visited northeast Syria to evaluate the mission against Islamic State and the risk to American personnel.

When asked at the time whether he thought sending about 900 American troops to Syria was worth the risk, Milley linked the mission to the safety of the country and its allies, responding: "If you think that's important, then the answer is "Yes".

"In my opinion, that is crucial, Milley said.

Hundreds of fighters are still encamped in desolate areas where neither the U.S.-led coalition nor the Syrian army, with support from Russia and Iranian-backed militias, exert complete control, even though Islamic State is a shadow of the organization that once ruled over a third of Syria and Iraq in a caliphate declared in 2014.

The Syrian Democratic Forces, which are led by Kurds and are America's main ally in the region, are guarding detention centers where thousands of additional Islamic State fighters are being held.

According to American officials, the Islamic State could still resurge as a significant threat.

The mission, which former President Donald Trump almost completed in 2018 before softening his withdrawal plans, is a holdover from the larger global war against terrorism that had previously included the war in Afghanistan and a much larger U.S. military deployment to Iraq, even though Islamic State is a shadow of the organization that once controlled over a third of the world.