At least five U.S. personnel were injured in an attack against a military base in Iraq on Monday, U.S. officials told Reuters, as the Middle East braced for a possible new wave of attacks by Iran and its allies following last week's killing of senior members of militant groups Hamas and Hezbollah.

Two Katyusha rockets were fired at al Asad airbase in western Iraq, two Iraqi security sources said. One Iraqi security source said the rockets fell inside the base. It was unclear whether the attack was linked to threats by Iran to retaliate over the killing of the Hamas leader.

The U.S. officials, who spoke to Reuters on condition of anonymity, said one of the wounded Americans was seriously injured. The casualty count was based on initial reports which could still change, they said.

"Base personnel are conducting a post-attack damage assessment," one of the officials added.

In a call on Monday, U.S. Secretary of Defense Lloyd Austin and Israeli Minister of Defense Yoav Gallant agreed that the attack marked "a dangerous escalation," according to a Pentagon readout.

Last week the U.S. carried out a strike in Iraq against individuals U.S. officials said were militants getting ready to launch drones and posed a threat to U.S. and coalition forces.

The U.S. has been watching to see if Iran would make good on its vow to respond to the killing of Haniyeh two days ago in Tehran, one in a series of killings of senior figures in the Palestinian militant group as the war between Israel and Hamas in Gaza rages.

The Pentagon has said it will deploy additional fighter jets and Navy warships to the Middle East, as Washington seeks to bolster defenses following threats from Iran and its allies Hamas and Hezbollah.

A rare ally of both the U.S. and Iran, Iraq hosts 2,500 U.S. troops and has Iran-backed militias linked to its security forces. It has witnessed escalating tit-for-tat attacks since the Israel-Hamas war erupted in October.

Iraq wants troops from the U.S.-led military coalition to begin withdrawing in September and to formally end the coalition's work by September 2025, Iraqi sources have said, with some U.S. forces likely to remain in a newly negotiated advisory capacity.