The officials say the suicide car bombing happened Monday outside a building housing a rapid response police unit.
Iraqi authorities deployed special police teams in Samarra to boost security for a Shi'ite pilgrimage earlier this month. Samarra is home to a gold-domed shrine of a 9th century imam revered by Iraqi Shi'ites.
In another development, authorities in northern Iraq say one person has been killed and scores wounded in fighting between Kurdish security forces and opposition activists protesting against the two ruling parties of the autonomous region.
Officials say security forces fired into the air in the city of Sulaimaniyah late Sunday, as more than 1,500 protesters denounced the political dominance of the Kurdistan Democratic Party and the Patriotic Union of Kurdistan. They say gunfire killed a 17-year-old demonstrator and wounded at least eight other people.
A previous protest outside the Kurdistan Democratic Party's Sulaimaniyah headquarters turned violent last Thursday, when security personnel fired at demonstrators, killing two and wounding many others.