BAGHDAD, July 1 (Reuters) – Iraqi Prime Minister Adel Abdul Mahdi issued a decree on Monday heavily curbing the powers of mostly Iranian-backed Shi’ite militias and forcing them to integrate more closely into the formal armed forces.

The militias, which helped Iraqi and U.S.-led international coalition forces to drive out occupying Islamic State militants under an umbrella grouping known as the Popular Mobilisation Forces (PMF), have broad influence in Iraqi politics.

An electoral alliance made up 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. Groups have until July 31 to abide by the new regulations.

The order came two weeks after three mortar shells landed on Balad military base, the first of several unclaimed attacks in recent days on bases in Iraq hosting U.S. forces and on a site used by a U.S. energy firm.

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

(Reporting by Ahmed Aboulenein; Editing by Kevin Liffey)