The US has launched air strikes against an Iran-backed militia in Iraq and Syria, the Pentagon announced.
The strikes hit "operational and weapons storage facilities", in response to drone attacks by the militia on US forces, a statement said, reports BBC.
"President Biden has been clear that he will act to protect US personnel," the Pentagon said.
This is the second round of airstrikes Joe Biden has authorised against Iran-backed militias since taking office.
US forces based in Iraq have been hit several times in recent months by drone attacks. Iran has denied any involvement.
Around 2,500 US troops are based in the country as part of an international coalition fighting the jihadist Islamic State (IS) group.
According to the Pentagon statement, the "defensive precision air strikes" hit two targets in Syria and one in Iraq. It said Iran-backed militia groups including Kataib Hezbollah and Kataib Sayyid al-Shuhada used these facilities.
Since 2009, the US has designated Kataib Hezbollah as a terrorist organisation, accusing them of threatening the peace and stability of Iraq.
The US acted in self-defence, the statement said, taking "necessary, appropriate, and deliberate action designed to limit the risk of escalation - but also to send a clear and unambiguous deterrent message".
The Pentagon did not say whether anyone was killed or injured in the attacks. But according to AFP news agency the Syrian Observatory for Human Rights, a UK-based monitoring group, said that five militia fighters were killed and several more wounded in Syria "in an attack by US warplanes".
Syrian state news agency Sana meanwhile reported that a child had died and at least three other people were wounded, AFP said.
Iran's influence over Iraq's internal affairs has grown steadily since the US-led invasion that toppled Saddam Hussein in 2003.
The strikes come as Iran has been holding talks with world powers including the US about reviving a 2015 nuclear deal, which lifted sanctions against the state in exchange for Iran stopping some nuclear work.
Some countries - including Israel - believe Iran is trying to build a nuclear bomb, something Iran denies.
Former US President Donald Trump unilaterally withdrew the US from the agreement in 2018 and reimposed sanctions.