Unidentified militants launched the assault on Tikrit on Tuesday, the same day the government of Iraq announced Mosul had been captured by the Islamic State of Iraq and Syria (ISIS).
An eyewitness told the BBC that the gunmen entered Tikrit from four different directions and set fire to a police station.
Clashes Wednesday between insurgents and security forces were reported in the city center.
Tikrit is also remembered as the hometown of Saddam Hussein.
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