Top U.S. officials said Wednesday that the United States would not "shy away" from responding to the latest rocket attack on U.S. and coalition personnel in Iraq with military force, if necessary.
Assailants launched rockets at the al-Asad air base in western Iraq's Anbar province early Wednesday, defense officials said, with at least 10 rockets hitting inside the compound.
One U.S. civilian contractor died after suffering a heart attack while taking shelter from the attack.
Pentagon press secretary John Kirby told reporters Wednesday that Iraqi security forces were leading the investigation, adding that it was still too early for any attribution.
"Let's let our Iraqi partners investigate this, see what they learn, and then if a response is warranted, I think we have shown clearly that we won't shy away from that," he said. "But we're just not there yet."
Kirby said the initial investigation indicated the rocket attack against al-Asad was launched from multiple locations to the east of the air base.
He also said the base's defenses, including a counter-rocket system, activated, although it was not yet clear whether the system hit any of the incoming devices.
Wednesday's incident at al-Asad was the latest in a series of rocket attacks by Iran-backed militias on bases in Iraq that house U.S. and coalition forces. It also came less than a week after U.S. President Joe Biden ordered an airstrike against a compound in eastern Syria, which U.S. officials said the militias had used to facilitate those attacks.
At the time, Biden said the strike was meant as a warning to Iran that it "can't act with impunity."
Speaking Wednesday at the White House about the attack on al-Asad, Biden told reporters the U.S. was "following that through right now."
"We're identifying who is responsible, and we'll make judgments from that point," he added.
The U.S. has blamed some of the previous rocket attacks on two Iran-backed militias - Kataib Hezbollah and Kataib Sayyid al-Shuhada. Officials said last week's strike was designed to make it more difficult for either group to carry out additional attacks.
"Certainly, this is a troubling development and not what anybody wanted to see," Kirby said Wednesday.
"Nobody wants to see the situation escalate," he added. "Just like before, we're going to act appropriately to defend our personnel, our interests and those of our Iraqi partners."
Other officials cautioned Washington's next move would be measured.
"If we assess a further response is warranted, we will take action again in a manner and time of our choosing," White House press secretary Jen Psaki told reporters. "What we won't do is make a hasty or ill-informed decision that further escalates [the situation] or plays into the hands of our adversaries."
Despite the U.S. rhetoric, one of the militias blamed for previous rocket attacks celebrated the attack on al-Asad.
"We congratulate the Iraqi resistance for the heroic operation on the base of evil in Ayn al-Assad," Abu Ali al-Aksari, a security official for Kataib Hezbollah, said in a statement issued Wednesday, translated by the SITE Intelligence Group.
"We advise our sons to continue this approach to expel the killers and scum from our sanctified land," he added, though he did not claim responsibility for the attack.
Al-Asad air base has been attacked before. Iran itself targeted the base last year in a retaliatory strike for the U.S. killing of top Iranian commander Qassem Soleimani.
Arrests in earlier attack
Separately, there appeared to have been some progress in efforts by officials in Iraq charged with tracking down those responsible for the February 16 rocket attack against Erbil International Airport, which killed a contractor and injured a U.S. servicemember.
The Kurdistan Region Security Council announced Wednesday that after working with both Iraqi federal authorities and the U.S.-led coalition, it had arrested two men involved in the attack.
Officials also released a video confession of one of the suspects, Haider Hamza.
In it, Hamza admitted to working with the Kataib Sayyid al-Shuhada militia, adding, "The rockets were made in Iran."
Iraqi Kurdistan counterterrorism officials have not yet named a second suspect, also in custody, and said a search was underway for two other men believed to have taken part in the Erbil attack.
Ahmad Zebari and Dilshad Anwar of VOA's Kurdish Service contributed to this report.