Secretary of State Antony Blinken exchanges challenge coins with the U.S. Marine Corps embassy security guard detachment in Baghdad, Iraq, on Nov. 5, 2023. JONATHAN ERNST / AP

Several U.S. service members were injured in a ballistic missile attack by Iranian-backed militias on Al-Asad Airbase in Iraq, Pentagon officials said Tuesday. The attack Monday night on U.S. and coalition forces involved a close-range ballistic missile and resulted in eight injuries and minor infrastructural damage, Brig. Gen. Pat Ryder, a Pentagon spokesperson, said in a statement.

U.S. military responded with a retaliatory strike, which was not pre-planned, killing several Iranian-backed militia personnel, CBS News learned.

"Immediately following the attack, a U.S. military AC-130 aircraft in the area conducted a self-defense strike against an Iranian-backed militia vehicle and a number of Iranian-backed militia personnel involved in this attack," Ryder said in his statement.

In a tweet, U.S. Central Command said the AC-130 "maintained visual confirmation of the individuals from the time of the launch to the time of engagement."

The U.S. conducted further "precision strikes" against two facilities in Iraq early Wednesday morning local time, CENTCOM said in a statement.

"The strikes were in direct response to the attacks against U.S. and Coalition forces by Iran and Iran-backed groups," including the attack on Al-Asad Airbase, "which involved use of close-range ballistic missiles," the statement read.

A U.S. official told CBS News the targets were an operations center and a communications node belonging to Kataib Hezbollah, one of the main Iran-backed militias in Iraq. The sites were manned at time of strikes, the official said, so casualties were expected. The official said there had been no retaliatory action by Kataib Hezbollah as of Wednesday morning.

The U.S. service members wounded in the attack are still being evaluated, a Pentagon official told CBS News, adding that this was the 66th attack against American-affiliated military bases in Iraq and Syria since Oct. 17.

The uptick in attacks comes amid international concern that the war between Israel and Hamas could broaden into a wider conflict engulfing the entire Middle East.

While Iranian-backed groups have targeted U.S. forces in Iraq and Syria with a mix of drones and rockets, this was the first time a short-range missile was used to attack American troops since Oct. 17, Deputy Pentagon Press Secretary Sabrina Singh said at a news conference Tuesday afternoon.

Of the 66 attacks in the last month, 32 were in Iraq and 34 in Syria, Singh said. The attacks have resulted in approximately 62 U.S. personnel injuries, Singh added — they do not include the injuries from Monday's attack.

"These groups in Iraq and Syria, that are attacking U.S. interests, have made their own decisions," Iranian Foreign Minister Amir-Abdollahian told CBS News last week when pushed on whether Iran backs militant groups in the Middle East.

"We have not taken anything off the table or ruled anything out," Singh said when asked if the U.S. will launch preemptive strikes to avoid further attacks. "We feel that we have taken appropriate action to decimate some of their facilities and some of their weapons, but again, we always reserve the right to respond at the time and place of our choosing."

Last month, Defense Secretary Lloyd Austin said that "the United States does not seek conflict and has no intention nor desire to engage in further hostilities, but these Iranian-backed attacks against U.S. forces are unacceptable and must stop."

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