Several U.S. service members and Iraq personnel were also wounded, the U.S.-led coalition fighting Islamic State said in a statement, adding that Iraqi security forces would be leading the response and investigation into the incident.
U.S. officials said, on condition of anonymity, that the service members were lightly wounded and believed to be back on duty.
One official said the United States was looking into the possible involvement of Kataib Hezbollah, an Iranian-backed Shi’ite Muslim militia group.
In December, U.S. Secretary of State Mike Pompeo blamed Iranian-backed forces for a series of attacks on bases in Iraq and warned Iran that any attacks by Tehran or proxies that harmed Americans or allies would be “answered with a decisive U.S. response.”
Tensions have heightened between Tehran and Washington since last year when President Donald Trump pulled the United States out of Tehran’s 2015 nuclear deal with six powers and reimposed sanctions that have crippled Iran’s economy.
Since then Washington has blamed Iran for attacks on oil tankers this summer, including off the coast of the United Arab Emirates, and a major strike on oil facilities in Saudi Arabia. Iran has denied being behind the attacks.
The Iraqi military said in a statement earlier on Friday that several rockets were launched into Iraq’s K1 military base, which houses U.S. and Iraqi forces. Security sources said security forces found a launchpad for Katyusha rockets inside an abandoned vehicle near the base.
No group has claimed responsibility for the attack.
Islamic State militants operating in the area have turned to insurgency-style tactics aimed at bringing down the government in Baghdad ever since it retook all territory and declared victory against them in December 2017.
However, a senior U.S. military official said this month that attacks by Iranian-backed groups on bases hosting U.S. forces in Iraq were gathering pace and becoming more sophisticated, pushing all sides closer to an uncontrollable escalation.
His warning came two days after four Katyusha rockets struck a base near Baghdad international airport, wounding five members of Iraq’s elite Counter-Terrorism Service, the latest in a spate of rocket strikes on bases hosting members of the U.S.-led coalition whose objective is to defeat Islamic State insurgents.
The K1 base, which lies 15 km (9 miles) northwest of Kirkuk, in northern Iraq, houses U.S. military forces alongside Iraqi forces from the Federal Police and Counter-Terrorism Service, security sources said. About 5,000 U.S. troops are in Iraq.