Joe Biden has ordered the first military attack of his presidency as the US carries out an airstrike in Syria.
Officials say the US carried out an airstrike against a target belonging to Iran-backed militia in response to recent rocket attacks against US targets in Iraq.
The Pentagon said the strikes destroyed a number of facilities at a border control point used by a number of Iranian-backed militant groups, including Kata'ib Hezbollah (KH) and Kata'ib Sayyid al-Shuhada (KSS).
It was not immediately clear if there were any casualties.
Pentagon spokesman John Kirby said: "At President Biden's direction, US military forces earlier this evening conducted airstrikes against infrastructure utilised by Iranian-backed militant groups in eastern Syria.
"President Biden will act to protect American and Coalition personnel. At the same time, we have acted in a deliberate manner that aims to de-escalate the overall situation in both eastern Syria and Iraq."
The airstrike comes after rockets hit the US military base at Erbil International Airport, Iraq on February 15, killing one non-American contractor and injuring a number of American contractors and a US service member.
Secretary of Defence Lloyd J. Austin said: "There's not much more that I'll be able to add at this point other than the fact that we're confident in the target we went after, we know what we hit.
"We're confident that the target was being used by the same Shia militia that conducted the strikes."
He added: "Let me say that I am very proud of the men and women in our force that carried out the strike. As you would expect, they performed in a very professional manner, and we are grateful for their service."
A US official, speaking on the condition of anonymity, said the decision to carry out these strikes was meant to send a signal that while the United States wanted to punish the militias, it did not want the situation to spiral into a bigger conflict.
Another salvo struck a base hosting US forces north of Baghdad days later hurting at least one contractor and rockets hit Baghdad's Green Zone on Monday which houses the US embassy and other diplomatic missions.
The KH group, one of the main Iran-aligned Iraqi militia group, has denied any role in the recent attacks.
Some Western and Iraqi officials say the attacks, often claimed by little-known groups, are being carried out by militants with links to KH as a way for Iranian allies to harass US forces without being held accountable.
It comes as Washington and Tehran look for a way to return to the 2015 nuclear deal abandoned by former US President Donald Trump.