The US military, under the direction of President Joe Biden, conducted airstrikes on Sunday against what it said were "facilities used by Iran-backed militia groups" near the border between Iraq and Syria.
Pentagon Press Secretary John Kirby said the militias were using the facilities to launch unmanned aerial vehicle attacks against US troops in Iraq.
Kirby said the US military targeted three operational and weapons storage facilities - two in Syria and one in Iraq.
He described the airstrikes as "defensive," saying they were launched in response to an "ongoing series of attacks by Iran-backed groups targeting US interests in Iraq."
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"The United States took necessary, appropriate, and deliberate action designed to limit the risk of escalation - but also to send a clear and unambiguous deterrent message," Kirby said.
US Air Force F-15 and F-16 jets were used to carry out the strikes, and returned to base without incident afterwards.
"At President Biden's direction, US military forces earlier this evening conducted defensive precision airstrikes against facilities used by Iran-backed militia groups in the Iraq-Syria border region," Kirby said.
"The targets were selected because these facilities are utilised by Iran-backed militias that are engaged in unmanned aerial vehicle (UAV) attacks against US personnel and facilities in Iraq.
"Specifically, the US strikes targeted operational and weapons storage facilities at two locations in Syria and one location in Iraq, both of which lie close to the border between those countries.
"Several Iran-backed militia groups, including Kata'ib Hezbollah (KH) and Kata'ib Sayyid al-Shuhada (KSS), used these facilities."