Iraqi Prime Minister Adel Abdul Mahdi has issued a decree curbing the powers of mostly Iranian-backed Shia militias and forcing them to integrate into Iraq’s formal armed forces – a politically risky move seemingly aimed at placating the United States.

“In the interest of the public good and as per the powers granted to us by the constitution … the following is decreed: All Popular Mobilisation Forces are to operate as an indivisible part of the armed forces and be subject to the same regulations,” the decree, issued on Monday, said.

The armed groups – known collectively as the Popular Mobilisation Forces (PMF) – helped Iraqi and US-led international coalition forces drive out occupying Islamic State of Iraq and the Levant (ISIL or ISIS) fighters, and now have broad influence in Iraqi politics.

An alliance of militia leaders and fighters came second in a 2018 parliamentary election.

The PMF already reports to the prime minister, who is the commander-in-chief of Iraq’s armed forces, but Abdul Mahdi’s decree forces groups that make up the PMF to choose between political and paramilitary activity.

Those who choose to integrate into the military must abandon their old names and sever ties to political organisations. Those who choose politics will not be allowed to carry weapons, the decree said.

Headquarters, economic offices, and checkpoints manned by militias are to be shut down.

Groups will be considered outlaws if they do not comply by July 31 with the new regulations, which come amid mounting tensions between the US and Iran, with Iraq seen as a possible site for any violent flare-up between the two rivals.

‘US concern’

Al Jazeera’s Mohammed Jamjoom, reporting from the Iraqi capital Baghdad, described the decree as “significant” and said it marked the latest in a series of moves by Abdul Mahdi’s administration concerning the PMF and “their workflow within the military establishment”.

“There has been concern, especially in the US, that there are factions within those groups that are affiliated with Iran and that they could pose a threat to Iraq and to US interests and personnel inside of Iraq,” Jamjoom said.

“Because of mounting tension in the region between the US and Iran, there is a lot of focus right now on these militia groups inside of Iraq that might be affiliated with Iran,” he added. “There has been building pressure on Abdul Mahdi to try to rein in Iranian influence inside of Iraq and to try to ensure that Iran does not play an oversized role right now in Iraq.”

Monday’s decree came two weeks after three mortar shells landed on Balad military base, the first of several recent unclaimed attacks on bases in Iraq hosting US forces, and on a site used by US oil giant ExxonMobil.

Local officials blamed the militias for one of the incidents, but Iran has not commented.

The US, meanwhile, evacuated hundreds of diplomatic staff from its embassy in Baghdad last month, citing unspecified threats from Iran, and has deployed thousands more troops to the Middle East since May.

Washington has also blacklisted Iran’s Revolutionary Guard Corps (IRGC), which has ties to a number of armed groups operating in Iraq, as a “terrorist group”. Iran has done the same to US forces operating in the Middle East.

US Secretary of State Mike Pompeo told Iraqi leaders during a surprise visit to Baghdad in May if they failed to keep in check Iran-backed militias, Washington would respond with force.