The US military’s Central Command on Wednesday announced that its forces conducted an airstrike that targeted areas used by militias backed by Iran’s paramilitary Revolutionary Guard. The strikes were targeted in Deir Ez-Zor, located in eastern Syria.

While announcing the airstrikes, Central Command spokesman Colonel Joe Buccino clarified that US President Joe Biden ordered the strike. Buccino said that “today’s strikes were necessary to protect and defend US personnel.

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Buccino added that the airstrikes were carried out in response to an August 15 attack targeting US forces. The US Central Command described the assault as causing “zero casualties and no damage” at the time.

That attack saw drones allegedly launched by Iranian-backed militias target the al-Tanf Garrison used by American forces, according to Associated Press reports.

American and coalition troops are based at al-Tanf to train Syrian forces on patrols to counter militants from the Islamic State group, the Washington Post reported earlier this month. The base is also located on a road serving as a vital link for Iranian-backed forces, stretching from Tehran all the way to Lebanon.

The US military’s Central Command said the strikes “took proportionate, deliberate action intended to limit the risk of escalation and minimize the risk of casualties.”

Tuesday’s airstrikes have not been acknowledged by Syrian authorities so far. Iran’s Revolutionary Guard has also not released any official statements.

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The strike was conducted in the Deir Ez-Zor area, which is a strategic province that borders Iraq and contains oil fields. The area, which is controlled by Syrian forces and Iran-backed militia, has seen frequent strikes from Israel.

US forces have maintained a constant presence in various Syrian provinces since 2015. The forces entered Syria to back allied forces in their fight against the Islamic State group.