Terrorists disguised as Iraqi security forces have killed seven people and injured 12 others on Saturday at a power plant north of the Iraqi capital of Baghdad, a security official said.

According to the official, three suicide bombers wearing military uniforms entered the facility in Samarra armed with grenades and explosive belts.

“They attacked the plant's workers, killing seven and wounding 12, according to an initial assessment,” the official told AFP on condition of anonymity.

ISIS, which frequently carries out suicide bombings in Iraq, claimed responsibility for the attack.

Two of the attackers were killed at the scene when security reinforcements arrived and evacuated the building.

“At 2am we were woken up by shots being fired,” Abdel Salam Ahmed, one of the employees who was shot in the legs, told AFP from his hospital bed.

“We ran into one of them (the terrorists). Some of us hid while two others kept running towards the exit, shouting ‘we are employees’, but they (the attackers) shot them dead,” he noted.

According to the AFP, prefabricated houses where employees were sleeping were destroyed in the explosion.

ISIS captured almost a third of Iraqi territories in 2014 when it declared a caliphate.

In recent months, the terrorist group has lost control over Iraqi cities.