The security forces, backed by Shia militias
, raised the Iraqi flag over the governorate and the main hospital buildings in the city Monday night, a security official with the forces in Tikrit told CNN.
The gains, according to the official, came after a slow advance into the city as the forces dealt with more than 300 improvised explosive devices planted in the city's streets.
At least 26 militants were killed in the operation, the official said. Earlier Monday, Iraqi federal police said in a statement aired on Iraqi television that the forces had liberated four neighborhoods in southern Tikrit.
The renewed push into Tikrit comes days after a series of U.S.-led airstrikes aimed at ISIS targets around the city
. The goal of those airstrikes was to pave the way for Iraqi forces to go in.
Now security forces and fighters from Hashd Al-Shaabi, a predominantly Shia paramilitary force that has doing much of the fighting in the critical battle to take Tikrit back from ISIS, say they're gaining ground.
Iraqi forces have tried multiple times to win back Tikrit since ISIS, which calls itself the Islamic State, conquered the city in June as part of its campaign to amass an expansive Islamic caliphate. And each time, so far, they've failed.
The latest push began after Iraqi Prime Minister Haider al-Abadi on March 1 ordered Iraqi forces to retake Tikrit and Salahuddin province. Militants have been under pressure ever since in the battleground city, which is the birthplace of former Iraqi dictator Saddam Hussein and located about 160 kilometers (100 miles) north of Baghdad.
ISIS responded by adjusting its positions in and around the city, hiding in buildings and other key infrastructure, said Saad al-Hadithi, a spokesman for al-Abadi. This movement led Iraq's military to pause its operation, out of growing worries that a full-on invasion could produce heavy Iraqi military and some civilian casualties.
The situation spurred the Iraqi Prime Minister to request help from the U.S.-led coalition, which conducted airstrikes around Tikrit last week.