Security forces declared curfew in Samarra without specifying its duration.
Two fighters were killed and eight others wounded from al-Hashd al-Shaabi – a pro-government Shiite militia – during a suicide explosion at one of the militia's bases.
The attack was followed by another suicide explosion which killed two people and wounded three others.
Seven people were also wounded in mortar strikes in several areas of Samarra city, the security source said.
Samarra is a city in the northern province of Saladin and has a Sunni majority. However, two Shiite shrines in the city make it a destination for Shiite visitors.
A security vacuum has gripped Iraq since June 2014, when ISIL stormed the northern province of Mosul and declared what it calls a caliphate in Iraq and Syria.