U.S. military action against three facilities along the Iraq-Syria border resulted in a number of casualties.
President Joe Biden directed attacks against three militia facilities used by several Iran-backed groups engaged in unmanned aerial vehicle (UAV) attacks against U.S. personnel and facilities in Iraq.
The strikes took place at approximately 6 p.m. Eastern Time Sunday, or 1 a.m. local time. The action, which Pentagon press secretary John Kirby described as "defensive," killed between four and seven militiamen.
Two Iraqi militia officials told the Associated Press that the first strike against a weapons storage facility inside Syrian territory killed four militiamen, but Britain-based group The Syrian Observatory for Human Rights reported the number was at least seven.
A U.S. defense official with knowledge of the strikes told Fox News that he did not expect "a lot of causalities" because of the time of the strikes.
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At least one facility used by Iran’s militia forces to launch and recover drones was destroyed, the official added. Recent strikes by the crude drones have targeted Americans in Baghdad and Erbil in northern Iraq.
Sunday's airstrikes are the latest operation carried out against Iranian-backed military groups, following President Biden's first known military action in February, when an airstrike targeted a compound in Syria operated by Kait’ib Hezbollah (KH) and Kait’ib Sayyid al Shuhada (KSS).
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Kirby claimed those same groups operated the facilities destroyed in Sunday’s action.
The Iran-backed Iraqi militia factions vowed revenge for the attack and said in a joint statement they would continue to target U.S. forces.
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"We ... will avenge the blood of our righteous martyrs against the perpetrators of this heinous crime and with God's help we will make the enemy taste the bitterness of revenge," the militias said.
Iraq's military condemned the strikes as a "blatant and unacceptable violation of Iraqi sovereignty and national security" in a rare condemnation of U.S. airstrikes.
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Senate Democrats have meanwhile urged Biden to explain the reason for the airstrikes, with Sen. Chris Murphy, D-Conn., saying he is concerned that "the pace of activity … is starting to look like what would qualify as a pattern of hostilities under the War Powers Act."
Fox News' Lucas Tomlinson and Lucas Manfredi and the Associated Press contributed to this report.