A massive explosion hit a key arsenal belonging to Iraq's Popular Mobilization Units (PMU) north of Baghdad on Aug. 19, the fourth and latest in a series of such attacks targeting the militia group's facilities in recent weeks.

The PMU came together in 2014 to tackle the rising threat of the Islamic State, which was making rapid advances to control large swaths of territory across Iraq. The Shiite-majority forces have since been backed and equipped by the government in neighboring Iran. The group is widely credited for its key role in the eventual defeat of the Islamic State and for helping flush the militant organization out of Iraq.

While no one has officially claimed responsibility for the recent attacks on the PMU interests, fingers of blame have already been pointed toward Israel. In a statement released Aug. 21, the PMU also implicated the Americans in the chain attack.  "The United States had allowed four Israeli drones to enter the region accompanying US forces and carry out missions on Iraqi territory," the statement read.

Israel has neither confirmed nor denied the accusations. Asked about the latest incident during a trip to Ukraine, Prime Minister Benjamin Netanyahu was brief and refused to address the strikes. "Iran has no immunity, anywhere," he said.