"Outraged by reports of another rocket attack on an Iraqi airbase," Pompeo tweeted. "These continued violations of Iraq's sovereignty by groups not loyal to the Iraqi government must end."

There was no immediate claim of responsibility for Sunday's rocket attacks, in which the Iraqi military said eight missiles wounded two Iraqi officers and two airmen.

The US has previously blamed such attacks on Iran-backed groups in Iraq.

The Al-Balad base had held a small US Air Force contingent as well as American contractors, but most were evacuated following a sharp rise in friction between the US and Iran over the past two weeks, military sources told AFP.

Al-Balad is the main airbase for Iraq's F-16s, which it bought from the US.

Military bases hosting US troops have been subject in recent months to rocket and mortar attacks that have mostly wounded Iraqi forces, but also killed one American contractor last month.

That death set off a series of dramatic developments, with the US carrying out deadly strikes against a pro-Iran paramilitary group in Iraq as well as a convoy carrying top Iranian commander Qasem Soleimani outside the Baghdad airport.

Pro-Iran factions in Iraq have vowed revenge for those raids.