Seven workers were killed when at least three attackers entered a power station and blew themselves up, Iraqi authorities said.
Eight security forces were injured in the suicide bombing in Samarra.
Brigadier General Yahya Rasool said two of the attackers disguised themselves as workers and a third wore a security forces uniform.
The attack happened at dawn on Saturday. No-one immediately claimed responsibility.
Electricity Ministry spokesman Musaab al-Mudaris said seven employees were killed and eight security forces were wounded. He put the number of attackers at four.
Mr Al-Mudaris said one attacker was shot dead, while the others blew themselves up.
Samarra is 78 miles north of the capital, Baghdad.