Iraqi troops and Shiite militias recaptured key parts of the refinery town of Beiji from ISIS Sunday, a general said.
The victory comes a day after Iraqi forces were able to withstand two attacks from ISIS in the hotly contested Anbar province Saturday.
The commander of the Interior Ministry's Quick Reaction Forces, Brig. Gen. Nassir al-Fartousi, told state TV that the Iraqi flag was raised on a local government building in Beiji and that troops were advancing to other areas, without elaborating.
The spokesman of Joint Operations Command, Brig. Gen. Saad Maan Ibrahim, said the security forces "are now controlling" the downtown Beiji area, describing the advance as an "important victory."
"The enemy has suffered a defeat and has sustained heavy losses and we hope that the whole city will be cleared within few days," Maan told The Associated Press in a brief interview, saying "dozens" of IS militants had been killed.
Beiji, some 155 miles north of Baghdad, fell to ISIS during its blitz across northern Iraq nearly a year ago, but parts of the town and nearby refinery have since been retaken by government forces. The town is strategically significant as it lies on the road to ISIS-held Mosul, Iraq's second largest city.
Iraqi and Kurdish forces have managed to roll back ISIS in many parts of the country with the help of U.S.-led airstrikes, and recaptured the northern city of Tikrit in April. But last month ISIS captured Ramadi, the provincial capital of the western Anbar province, in the extremists' most significant advance since last year.
ISIS has declared an Islamic caliphate in the territories it controls in Syria and Iraq, and has used oil facilities and smuggling to finance much of its operations.
In neighboring Syria, the U.S.-led coalition carried out airstrikes against ISIS positions in the northern town of Souran, which ISIS captured last week from Syrian rebel groups and members of Al Qaeda's affiliate in Syria, the Nusra Front.
The Local Coordination Committees and the Britain-based Syrian Observatory for Human Rights said the airstrikes occurred Saturday night. The Observatory said the airstrikes killed eight ISIS members, including a local Syrian commander, and wounded 20.
The coalition airstrikes against ISIS in Souran were the first in the area since the extremist group launched an offensive last month on the northern parts of Aleppo province close to the border with Turkey. IS has captured several villages and towns from the Nusra Front and Syrian rebels.
Since September, the coalition has carried out hundreds of airstrikes against ISIS in Syria. The coalition has also carried out a handful of airstrikes against the Nusra Front. The U.S. says it has targeted a Nusra Front cell plotting attacks on Western interests.
The main Western-backed opposition group, the Syrian National Coalition, says government warplanes have been attacking rebels in Aleppo province, claiming that the "terrorist interests" of President Bashar Assad's government and the IS group are aligned.
In the northeastern city of Hassakeh, government forces have launched a counteroffensive and regained ground lost to IS last week, state media said. State news agency SANA said government forces have retaken the power station south of Hassakeh as well as the juvenile prison that had been recently seized by the ISIS.
In Saturday's attack, government forces and Shiite militiamen used anti-tank missiles to stop four would-be suicide car bombers, officials said.
ISIS fighters attacked the government held town of Husseiba with heavy mortar fire early Saturday, police and military officials said. They say attackers retreated after an hours-long battle, leaving behind three destroyed vehicles and five dead fighters. At least 10 troops and militiamen were wounded in the clash.
Elsewhere in the Anbar province, officials said Iraqi troops using Russian anti-tank Kornet missiles destroyed four incoming suicide car bombs during an attack in the Tharthar area.
The Associated Press contributed to this report.