Iraqi forces have launched a campaign to retake a key area north of the capital Baghdad and dislodge Islamic State militants.
The operation came as a group of suicide bombers targeted a military headquarters in western Iraq, killing eight officers on. No one immediately claimed responsibility.
The Joint Operations Command said the "new offensive" began at dawn in an agricultural area north-east of the city of Samarra, 60 miles north of Baghdad, with the aim to cut IS supply lines and to tighten the grip around the IS-held northern city of Mosul.
The command said paramilitary forces, mostly Shiite militias, and the Iraqi air force were backing the push. The statement did not say whether the US-led international coalition was involved in the operation.
Controlling the Jazerat Samarra area will not only restrict the IS militants' movements between the three provinces in the region, but will also be essential for future operations to retake parts of Anbar province and Mosul, said Sabah al-Numan, spokesman of the counter-terrorism forces.
He said two vehicles loaded with militants were bombed today, and that the security forces managed to hit a would-be suicide car bomber before he reached his target.
The offensive comes on the heels of two massive bombings in as many days by the IS group in the area - in the town of Muqdadiyah and in Baghdad - that killed at least 110 people.
Shiite paramilitary spokesman Ahmed al-Asadi said the offensive "is in retaliation for the blood of our martyrs and to annihilate the terrorist gangs that have wreaked havoc".
Meanwhile, four suicide bombers disguised in army uniform struck at dawn at the military headquarters in the city of Haditha, 150 miles north-west of Baghdad, killing eight troops, including a local army commander.
One of the bombers first attacked the gate of the building, then the others blew up themselves up when people gathered at the scene to help the victims. Eight soldiers were also wounded in the attack.
IS still controls much of northern and western Iraq, but has been driven back in recent months in some areas, such as the cities of Ramadi and Tikrit.
The government last month declared the western city of Ramadi, the Anbar provincial capital, "fully liberated" after it had been captured by IS last year.
Iraqi ground offensives - despite heavy backing from US-led coalition air strikes - have been slow in scoring key victories against IS. A campaign to retake Mosul, the main city held by IS in Iraq, has long been believed to be imminent but has not begun yet.