Iraqi military vehicles military fired machine guns and mortars toward Tikrit General Hospital believed to be used as a shelter by extremists.
Smoke was seen rising from the hospital and surrounding buildings, as helicopters flew overhead.
The final push in the battle to drive ISIS from the city, however, is going ahead without the Shiite militias, which had been instrumental to the operation so far and which backed out in protest over the US involvement in the fight for Tikrit.
On Wednesday, the US began airstrikes in Tikrit in support of what it called a "stalled" Iraqi ground offensive to retake the city.
The US initially did not provide air support in Tikrit because Baghdad pointedly chose instead to “partner with Iran”, AP reports.
Representatives of the Shiite militia said they chose to withdraw from the battle for Tikrit in protest of the United States entering the fray.