BEIRUT (AP) — The U.S. military said early Wednesday it carried out airstrikes in eastern Syria that targeted areas used by militias backed by Iran’s paramilitary Revolutionary Guard.

Opposition war monitor the Syrian Observatory for Human Rights and activist collective Deir Ezzor 24 said the airstrikes targeted the Ayash Camp run by the Fatimiyoun group made up of Shiite fighters from Afghanistan. The war monitor reported that at least six Syrian and foreign militants were killed in the airstrikes, while Deir Ezzor 24 reported 10 deaths.

Deir Ez-Zor is a strategic province that borders Iraq and contains oil fields. Iran-backed militia groups and Syrian forces control the area and have often been the target of Israeli war planes in previous strikes.

In Iran, Foreign Ministry spokesman Nasser Kanaani issued a statement later Wednesday condemning the American strike “against the people and infrastructure of Syria.” He also denied that Iran had any link to those targeted. Iran routinely denies arming militia groups targeting U.S. forces in the region, despite weaponry linking back to them.

The U.S. military’s Central Command said the strikes “took proportionate, deliberate action intended to limit the risk of escalation and minimize the risk of casualties.” It did not identify the targets, nor offer any casualty figures from the strikes, which the military said came at the orders of President Joe Biden.

“Today’s strikes were necessary to protect and defend U.S. personnel,” Central Command spokesman Col. Joe Buccino said in a statement.

The U.S. Treasury said the the Fatimiyoun has fought numerous battles in Syria, and is led by Iran’s elite Quds Force of the Revolutionary Guard.

“The Ayash warehouse is a very important one for Iran’s militias,” Deir Ezzor 24 CEO Omar Abu Layla told The Associated Press. “We expect that Iran will respond, either in al-Tanf or possibly in Iraq.”

Buccino added the attack was in response to an Aug. 15 attack targeting U.S. forces. That attack saw drones allegedly launched by Iranian-backed militias target the al-Tanf Garrison used by American forces. U.S. Central Command described the assault as causing “zero casualties and no damage” at the time.

There was no immediate acknowledgment by Syria’s state-run media of the strikes hitting Deir Ez-Zor.

U.S. forces entered Syria in 2015, backing allied forces in their fight against the Islamic State group.