BAGHDAD/WASHINGTON - Tensions between the United States and Iran simmered on Wednesday after a new rocket attack against Iraq's Ain al-Asad air base that hosts US forces, which US officials told Reuters fit the profile of a strike by Iran-backed militia.
There were no reports of injuries among US service personnel but an American civilian contractor died after suffering a "cardiac episode" while sheltering from the rockets, the Pentagon said.
President Joe Biden said US officials were examining the incident closely.
"Thank God no one was killed by the rocket ... We're identifying whose responsible and we'll make judgments at that point," Biden told reporters before a meeting with lawmakers in the Oval Office.
Iraqi officials said 10 rockets landed at the base but the Pentagon was more guarded, saying there were 10 "impacts." It said the rockets appeared to have been fired from multiple sites east of the Iraqi base, which was targeted last year by a ballistic missile attack directly from Iran.
In February, there were three rocket attacks in Iraq in just over a week that targeted areas that host US troops, diplomats or contractors. One attack on February 16 on US-led forces killed a civilian contractor and injured a US service member.
US officials, speaking on condition of anonymity, said the latest strike fit the profile of an attack by Iran-backed militia but the Pentagon said it was too soon to come to any conclusions.
"We cannot attribute responsibility at this time, and we do not have a complete picture of the extent of the damage," Pentagon spokesman John Kirby added. No group immediately claimed responsibility for the attack.
The United States is assessing the impact of the attack and whoever was responsible, White House spokeswoman Jen Psaki said.
"If we assess that further response is warranted, we will take action again in a manner and time of our choosing," she told a news briefing.
"What we won't do is make a hasty or ill-informed decision that further escalates the decision or plays into the hands of our adversaries."
Last Thursday, US forces carried out air strikes against facilities at a border control point in Syria used by Iranian-backed militias including Kata'ib Hezbollah and Kata'ib Sayyid al-Shuhada.
A Baghdad Operations Command official said Wednesday's attack was launched from a location about eight km (five miles) from the base, which is in the westerly Anbar province.
Another Iraqi security source and a government official who spoke on condition of anonymity said the rockets had been launched from a point west of the nearby town of Baghdadi.
Despite a deterioration in security in some parts of the country, Pope Francis is due to begin a four-day visit to Iraq on Friday.