Unidentified drones have attacked a base in Iraq’s Salahudin Province belonging to Popular Mobilization Forces (PMU), television network reported.

The attack killed one PMU member and injured another four, Iraq’s al-Ahad television network reported on Friday.

Footage later released by Iraqi media from the assault’s aftermath showed a large flame in what was reportedly a PMU base near the town of Amerli.

It is yet unclear who orchestrated the operation.

Meanwhile, the Iraqi al-Etejah television network reported that an American B350 reconnaissance plane had flown over the region a few days earlier.

The PMU — better known as Hashd al-Sha’abi — was formed by popular volunteer forces in 2014 after the Daesh Takfiri terror group launched a campaign of bloodshed and destruction against the nation.

It joined forces with the national army and effectively contributed to its anti-terror operations. The combined push, which was reinforced by Iraq’s allies, including Iran, ultimately led to Daesh’s expulsion in late 2017.

The Iraqi parliament on November 26, 2016 approved a law giving full legal status to Hashd al-Sha’abi fighters. Last March, the then prime minister, Haider al-Abadi, to order the PMU’s formal inclusion in the Arab country’s army.

The order would grant the PMU many of the same rights as members of the military, but it is yet to be fully implemented.

Earlier this month, Abadi’s successor, Adil Abdul-Mahdi, issued a decree, calling for the PMU’s full integration in the Iraqi military.

The attack on the Hashd al-Sha’abi base comes as the United States has sought to pressure Baghdad against the PMU.

Washington has often labeled Iraqi units operating under the PMU organization as being “Iran-led terrorists groups,” a claim denied by the Iraqi officials.

Iraqis have sharply rejected Washington’s hostile stance against Hashd al-Sha’abi forces, describing it as a violation of the Arab country’s sovereignty.