Updated

The U.S. military carried out an airstrike against an Iranian-backed militia stronghold in Syria Thursday, a senior official told Fox News.

In the first known military action by President Biden, multiple facilities were struck by American F15 fighter jets that targeted Iraqi border-based Shia militia groups, Kait’ib Hezbollah and Kait’ib Sayyid al Shuhada.

Both forces are suspected of having received funding and military support from Iran’s Islamic Revolutionary Guard.

The senior official said the strike was "shot across the bow" and a defensive strategy, intended to deter Iran and its militia from launching rockets at U.S. forces in the region, like the recent attacks in Iraq.

The Defense Department later confirmed the strikes.

"These strikes were authorized in response to recent attacks against American and coalition personnel in Iraq, and to ongoing threats to those personnel," Pentagon Press Secretary John Kirby said Thursday.

IRAQ ROCKET ATTACK KILLS CONTRACTOR, WOUNDS US SERVICE MEMBER, COALITION SAYS

Two rockets landed within the U.S.’s Green Zone in Baghdad Monday, falling near the U.S. embassy and marking the third attack of its kind within a week.

The Green Zone is several miles wide and houses the U.S. embassy and other government buildings.

Though Monday’s strike reported no casualties, a rocket fired in Erbil, Iraq last week killed several people; an American service member and multiple American contractors were injured. 

"We are outraged by the recent attacks," State Department spokesman Ned Price said Monday.

"When it comes to our response, we will respond in a way that is calculated, within our own timetable, and using a mix of tools at a time and place of our choosing," he added. "What will not do is lash out and risk an escalation that plays into the hands of Iran and contributes to their attempts to further destabilize Iraq."

POMPEO REACTS TO SYRIA AIRSTRIKES 

The Pentagon said the defensive strike Thursday was conducted with diplomatic support and in coordination with coalition partners.

At least one fighter was killed, according to reports citing an Iraqi militia official. Reuters, citing local sources, also reported that at least 17 were dead, while The Associated Press quoted the Syrian Observatory for Human Rights as saying 22 fighters were killed -- but neither death toll could be confirmed. 

Elsewhere, Russia’s Foreign Ministry on Friday condemned the strikes. 

"We call for the unconditional respect of the sovereignty and territorial integrity of Syria," spokeswoman Maria Zakharova said, according to Reuters.  

The airstrike was timed to avoid large-scale casualties and targeted a command hub. The extent of the damage and casualties hit will be known after a bomb assessment is complete, security officials told Fox News. 

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"The operation sends an unambiguous message -- President Biden will act to protect American coalition personnel," Kirby told reporters Thursday.

"At the same time, we have acted in a deliberate manner that aims to deescalate the overall situation in both Eastern Syria and Iraq," he added.

Fox News' Lucas Tomlinson and Greg Norman contributed to this report.