At least four Iraqi soldiers were wounded Sunday in an attack on the Balad air base in northern Iraq, according to Reuters.

The outlet cited the Iraqi military as saying in a statement that the base, which also houses US personnel and is located about 50 miles north of Baghdad, was targeted by eight Katyusha rockets. According to the report, seven of those rockets hit the base's runway.

No casualties among the US forces were reported, according to Reuters, and the military statement did not identify who was behind the attack.

The injuries came just days after an attack on two military bases in Iraq that house US forces that were launched by Iran in retaliation for the killing of Maj. Gen. Qassem Soleimani, the high-profile head of the elite Quds Force of Iran's Revolutionary Guard Corps.

US Secretary of State Mike Pompeo tweeted to say he was "outraged" by the attack and called on the Iraqi government "to hold those responsible for this attack on the Iraqi people accountable."

In a subsequent tweet, Pompeo wrote: "These continued violations of Iraq's sovereignty by groups not loyal to the Iraqi government must end."

The killing of Soleimani immediately triggered security concerns for US entities in the region, as Iran's supreme leader, Ayatollah Ali Khamenei, said a "harsh retaliation is waiting" for Americans.

The Pentagon has for the most part given vague justifications over why it targeted Soleimani, saying he "was actively developing plans to attack American diplomats and service members in Iraq and throughout the region."