US Secretary of State Mike Pompeo early Monday morning said he was“outraged” by the rocket attack targeting Al-Balad, an airbase just north of Baghdad where US forces have been stationed, which wounded two Iraqi officers and two airmen.

“Outraged by reports of another rocket attack on an Iraqi airbase,” he tweeted. “I pray for speedy recovery of the injured and call on the Government of Iraq to hold those responsible for this attack on the Iraqi people accountable.”

“These continued violations of Iraq’s sovereignty by groups not loyal to the Iraqi government must end,” he added.

A volley of rockets slammed into the Iraqi airbase north of Baghdad where US forces have been based, sources in the Iraqi military had said on Sunday.

Its statement said eight Katyusha-type rockets landed on Al-Balad airbase, wounding two Iraqi officers and two airmen. Reuters, quoting military officials, identified the wounded as Iraqi soldiers.

The attack by at least six rockets on Sunday came just days after Iran fired ballistic missiles at two bases in Iraq that house US forces, causing no casualties.

In a briefing to parliament, Hossein Salami, commander of Iran's Revolutionary Guards, said the missiles it fired last Wednesday on Iraqi bases hosting US troops were not aimed at killing American personnel.

No group claimed responsibility for Sunday's attack, according to Associated Press.

The US and Iran recently stepped back from escalating tensions following the killing of Genernal Qassem Soleimani, Iran’s top general, in a US airstrike in Baghdad. A senior Iraqi leader was also killed.

Iran’s retaliatory attack for Soleimani’s death hit two Iraqi bases, Ain al-Asad and Irbil, where American troops are based.

The limited Iranian strikes appeared to be mainly a show of force, and de-escalated tensions that had threatened to turn Iraq into a proxy battlefield.