Sixteen others were wounded in the blast that set fires on both sides of a commercial street in the heart of the city, according to an Iraqi army officer, who requested anonymity in line with military regulations. Tikrit's main hospital said it had received several patients wounded in the attack.
There were no immediate claims for the attack, but the Islamic State group has claimed responsibility for several recent attacks, including a string of bombings around the capital Baghdad earlier this month, and an attack on the house of a security official in western Iraq that killed 9 people.
The militant group has switched to insurgent tactics since it was defeated in Iraq's urban centers last year.
Tikrit is the capital of Iraq's northern Salahuddin province, where security forces killed 30 Islamic State militants in a raid in October. Another 20 militants were killed in a raid in the nearby Makhmour Mountains the next day.
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