"At President Biden's direction, US military forces earlier this evening conducted airstrikes against infrastructure utilized by Iranian-backed militant groups in eastern Syria," said spokesman John Kirby in a statement.

"These strikes were authorized in response to recent attacks against American and Coalition personnel in Iraq, and to ongoing threats to those personnel," he said.

The US military did not say whether there were any casualties in Thursday's attack.

Kirby said the target was a border control point used by Iranian-backed armed Iraqi groups including Kataeb Hezbollah and Kataeb Sayyid al-Shuhada.

It followed three rocket attacks on facilities in Iraq used by US and coalition forces fighting the Islamic State group.

One of those strikes, on a military complex in the Kurdish region's capital Arbil on February 15, killed a civilian and a foreign contractor working with coalition forces, and injured several US contractors and a soldier.

The attacks in Iraq by groups believed operating under Iran's direction had laid down a challenge to the new Biden administration just as it opened a door to resumed negotiations with Tehran over its nuclear program.

The Biden administration says it wants to revive the 2015 accord designed to freeze Iran's nuclear development.

But it also sees Tehran as a continuing security threat across the Middle East.

Kirby called Thursday's strikes "proportionate" and said it "was conducted together with diplomatic measures," including consultation with US partners in the anti-IS coalition.

But he also said that it was designed to de-escalate the situation in eastern Syria and Iraq.

"The operation sends an unambiguous message: President Biden will act to protect American and Coalition personnel," he said.