Iraqi forces and tribal fighters Saturday beat back a fresh assault by Sunni militants on the town of Haditha, strategic for the large nearby dam and its oil refinery, police said.
Battles also erupted Saturday in the central province of Diyala as security forces fought back against militants who have seized swathes of territory and a string of towns and cities in an offensive launched on June 9.
The violence comes a day before Iraq's deeply-divided politicians are to hold a parliament session aimed at reviving flagging efforts to form a government in the face of the jihadist-led onslaught.
The attack on Haditha, located northwest of Baghdad in Anbar province on the road linking militant-held western areas and the provincial capital, began with mortar fire, police said.
Gunmen travelling in vehicles, including some captured from security forces, then attacked from two sides but were kept from entering the town in fighting that left 13 militants and four police dead, officers and a doctor said.
While there have been previous attacks on Haditha, they have not been on this scale. Capture of the dam by the militants would raise the prospect of it being used to flood towns and villages downstream.
Militants earlier this year caused major flooding by releasing water from another dam in Anbar province.
In Diyala province, meanwhile, security forces and civilian volunteers Saturday launched a push to retake militant-held areas north of Muqdadiyah, a town on a main road to provincial capital Baquba, a police captain said.
In the town of Jalawla, also in Diyala, Kurdish peshmerga fighters began a major operation to expel militants from areas they hold, a senior Kurdish officer said.
Major General Hussein Mansur said Kurdish forces were using tanks and artillery in the battle, and had succeeded in retaking some territory from the militants.
Security forces folded during the initial offensive led by the Islamic State jihadist group, prompting the government to announce that it would arm civilian volunteers, thousands of whom have since signed up.
While security forces have since improved, they are still struggling to make significant gains in offensive operations, and a major push to retake executed dictator Saddam Hussein's hometown Tikrit has made little progress in more than two weeks.
As federal security forces quit their posts in northern areas during the initial fighting, Iraqi Kurds took control of a swathe of disputed territory that they have long wanted to incorporate into their autonomous region over Baghdad's strong objections.
While they have kept areas from being overrun by militants, the move has caused a major escalation in tensions between the Kurdish region and the federal government.
Kurdish authorities on Friday laid claim to disputed northern oilfields in a move slammed by Baghdad, further raising the stakes.
The Baghdad-Kurd row has dimmed the prospects of significant progress in forming a new government when parliament meets on Sunday.