The United States military has carried out "precision defensive strikes" against Iranian-backed paramilitaries in Iraq and Syria.
Five facilities controlled by the Kata'ib Hezbollah group were successfully targeted, in response to repeated attacks on Iraqi military bases hosting US forces. An Iranian militia organisation said that at least 19 people were killed during the US strikes on Sunday.
Last week, over 30 rockets targeted a base near Kirkuk, northern Iraq, killing an American civilian contractor.
A spokesman for the US Department of Defense said the retaliation will "degrade" the Iran-backed paramilitary group's "ability to conduct future attacks" against Operation Inherent Resolve (OIR) coalition forces.
Jonathan Hoffman said the OIR coalition "is in Iraq at the invitation of the Iraqi government to ensure the lasting defeat of ISIS", but "will not be deterred from exercising its right of self-defense".
Iraq's Joint Operations Command said in a statement that three US air strikes on Sunday evening hit the headquarters of the Hezbollah Brigades at the Iraq-Syria border, killing four fighters.
Iraq's Hezbollah Brigades, as Kata'ib Hezbollah is also known, is a separate force from the Lebanese group Hezbollah. It operates under the umbrella of the state-sanctioned militias known collectively as the Popular Mobilisation Forces. Many of them are supported by Iran.
During the air strikes, the US hit three of the militia's sites in western Iraq and two in eastern Syria - including weapon depots and the militia's command and control bases.
The strikes were carried out by US Air Force F-15 Strike Eagle aircraft and were declared a success by US Secretary of Defense Mark Esper.
"The strikes were successful. The pilots and aircraft returned back to base safely", he said.
"I would note also that we will take additional actions as necessary to ensure that we act in our own self-defense and we deter further bad behaviour from militia groups or from Iran."
However, the Kata'ib Hezbollah group has vowed to get revenge for the "aggression of evil American ravens".
In Tehran, Iran's foreign ministry spokesman Abbas Mousavi condemned the US strikes as an "obvious case of terrorism" and accused Washington of ignoring Iraq's sovereignty.
Cover image: F-15E Strike Eagle aircraft similar to those involved in the US strikes (Picture: US Department of Defense).