Iraq’s Hashd al-Shaabi military force said Monday that 22 of its members had been killed in airstrikes carried out by U.S.-led coalition warplanes near Iraq’s border with Syria.

Axar.az reports citing SANA.

Incorporated into the Iraqi Armed Forces in late 2016, the Hashd al-Shaabi is composed mainly of Shia fighters.

In a statement, the group said that U.S. warplanes had struck one of its encampments near the Syrian border, leaving 22 of its fighters dead.

The statement went on to demand a “formal explanation” from the U.S. regarding the deadly incident.

First established in 2014 with the express purpose of fighting the Daesh terrorist group, the Hashd al-Shaabi is believed to include more than 150,000 Shia fighters.