The rocket fire on Monday was the latest in a series of attacks targeting Ain al-Assad base, which hosts American troops as well as personnel from the US-led coalition against the Islamic State jihadist group.

"There was a suspected rocket attack today against US and coalition forces" at the site in western Iraq, a US defence spokesperson said. "Initial indications are that several US personnel were injured."

"Base personnel are conducting a post-attack damage assessment" and updates will be provided as more information becomes available, the spokesperson added.

US President Joe Biden and Vice President Kamala Harris were briefed on the attack, the White House said.

"They discussed the steps we are taking to defend our forces and respond to any attack against our personnel in a manner and place of our choosing," it said in a statement.

The Iraqi authorities said Tuesday that two rockets were fired at the base.

Security forces seized a truck with eight rockets ready for launch and were pursuing the perpetrators of the attack, the government's security media unit said.

Earlier, an Iraqi military source spoke of multiple rockets, while a commander in a pro-Iran armed group told AFP that at least two rockets targeted the base, without saying who was responsible.

Such attacks were frequent early in the war between Israel and Hamas Palestinian militants in Gaza but since then have largely halted.

The latest rocket fire comes as fears grow of an attack by Iran and its allies on Israel in retaliation for the killing of top Hamas and Hezbollah figures in strikes last week either blamed on or claimed by Israel.

- Series of attacks -

The killings are among the most serious series of tit-for-tat attacks that have heightened fears of a regional conflagration stemming from the Gaza war.

The Iran-aligned "Axis of Resistance" against Israel, which also includes Iraqi groups and Yemen's Huthis, has already been drawn into the nearly 10-month war.

Monday's rocket attack occurred after US forces carried out a strike last week on combatants who were attempting to launch drones that were deemed a threat to American and allied troops, a US official said.

The strike, which Iraqi sources said left four killed, was the first by American forces in Iraq since February.

The Iraqi security media unit reiterated the "strong objection to any aggression, whether from inside or outside Iraq, on Iraqi territories, interests and targets.

"We reject all reckless actions against Iraqi bases, diplomatic missions, and locations of the international coalition advisors, as well as anything that could escalate tension in the region or drag Iraq into dangerous situations," it added.

Iraqi territory must not be used for "settling scores" that would lead to war, it said.

There have been two recent attacks targeting bases hosting US and allied forces in Iraq -- on July 16 and 25.

Prior to that, US troops in Iraq and Syria had not been targeted since April. But attacks against them were much more common in the first few months of the Israel-Hamas war in Gaza, when they were targeted more than 175 times.

The Islamic Resistance in Iraq, a loose alliance of pro-Iran groups, claimed the majority of the attacks, saying they were in solidarity with Palestinians in Gaza.

In January, a drone strike blamed on those groups killed three US soldiers at a base in Jordan. In retaliation, US forces launched dozens of strikes against Tehran-backed fighters in Iraq and Syria.

Baghdad has sought to defuse tensions, engaging in talks with Washington on the future of the US-led coalition's mission in Iraq, with Iran-backed groups demanding a withdrawal.

The US military has around 2,500 troops in Iraq and 900 in Syria.