In Salahudin province, the security forces backed by some allied militias made further advance inside the IS-held provincial capital city of Tikrit after fierce clashes with the militants during the day, a provincial security source told Xinhua on condition of anonymity.
The troops retook control of the main hospital building on the southeastern edge of the city and took new positions in the surrounding area as they are heading toward the central part of Tikrit, which located some 170 km north of the Iraqi capital of Baghdad, the source said.
The troops also made another advance in Dyoum district in the western part of Tikrit after heavy bombardment by artillery and aircraft, the source added.
Late on Wednesday, Iraqi Prime Minister Haider al-Abadi announced that the Iraqi forces started the final phase to liberate Tikrit and the rest of the northern parts of Salahudin province with the assistance of the international coalition air support.
The battles to free Tikrit from IS militants were stalled for about two weeks as the militants planted thousands of bombs and booby-trapped dozens of buildings and cars.
Since March 2, some 30,000 Iraqi troops and thousands of allied Shiite and Sunni militias have been involved in Iraq's biggest offensive to recapture the northern part of Salahudin province, including Tikrit and other key towns and villages, from IS militants.
Large parts of the province have been under IS control since June 2014, after bloody clashes broke out between Iraqi security forces and the group.
In Anbar province, the security forces repelled an attack by the IS militants on an military base in north of the militant-seized city of Fallujah, some 50 km west of Baghdad, after heavy clashes with the attackers, a provincial security source told Xinhua on condition of anonymity.
The IS attack started when a suicide bomber blew up an armored vehicle packed with explosives at the entrance of the base and was followed by dozens of IS militants who faced stubborn resistance from the soldiers and allied militiamen of the Hashid al-Shaabi, or Popular Mobilization members, the source said.
The battle resulted in the killing of four militiamen and three soldiers and the wounding of nine security members, the source added.
Separately, the IS militants carried out an attack to seize a bridge in north of Fallujah, but were also repelled by the security forces and U.S.-led coalition aircraft which destroyed two of the IS vehicles carrying heavy machine guns, killing nine extremist militants aboard, the source said.
The IS group has seized parts of Iraq's largest province Anbar and tried to advance toward Baghdad, but several counter attacks by security forces and Shiite militias have pushed them back.
The security situation in Iraq has drastically deteriorated since June 10 last year, when bloody clashes broke out between Iraqi security forces and the IS.