There was no immediate claim of responsibility for the strike at Balad airbase, which caused no casualties or property damage, but the US routinely blames Iran-linked Iraqi factions for such attacks on its troops and diplomats.

Sunday's was the 14th attack against American interests -- including troops, the Baghdad embassy or Iraqi supply convoys to foreign forces -- since US President Joe Biden took office in January.

Two Americans and an Iraqi civilian have been killed in the attacks.

An Iraqi civilian working for a firm maintaining US fighter jets for the Iraq airforce was also wounded in one attack.

The operations are sometimes claimed by obscure groups experts say are smokescreens for Iranian-backed organisations long present in Iraq.

Qais al-Khazali, a senior pro-Iran figure in the state-sponsored Hashed al-Shaabi paramilitary force, recently declared that the "resistance" was carrying out attacks and would step them up "unless the US withdraws all its combat forces from across Iraq".

- Balancing interests -

The latest attack came as Washington prepares to launch a strategic dialogue with the government of Prime Minister Mustafa al-Kadhemi, who has regularly received threats from pro-Iran factions.

Kadhemi faces the delicate task of balancing the interests of neighbouring Iran and the US, arch-rivals who are both deeply involved in Iraqi politics.

Washington on Wednesday extended by several months a sanctions exemption allowing Iraq to import electricity from Iran during the ferociously hot summers when air-conditioning sends demand spiking.

The US, which led a coalition from 2014 to oust the Islamic State group from its self-declared "caliphate" in northern Iraq and Syria, still has some 2,500 troops in Iraq.

Since the defeat of their shared enemy, Washington and pro-Iranian factions have exchanged both threats and fire.

In February, the US carried out a raid against pro-Iranian Iraqi fighters in Syria. The Syrian Observatory for Human Rights war monitor reported 22 of them had died, while the Pentagon reported just one death.

Joe Biden's administration has stressed that the action was meant as a warning and to avoid further escalation of tensions between Tehran and Washington.

Pentagon spokesman John Kirby said Washington wanted to "send a very strong signal that we're not going to tolerate attacks on our people and our Iraqi partners".

But both sides are wary after a previous escalation in January 2020, sparked by the US assassination of top Iranian general Qasem Soleimani, took the arch-enemies to the brink of war.