Up to 11 people were killed and some 70 wounded on Monday when a suicide bomber struck the police headquarters in Tikrit, capital of Salahudin province, a provincial police source told Xinhua.
"The final reports said that 11 were killed, including eight policemen, and 70 people were wounded by the blast," the source said on condition of anonymity.
Many of the wounded were civilians who sustained injuries either directly from the explosion or from flying splinters of window panes of nearby houses and shops, the source added.
The suicide bomber blew up an explosive-laden tanker truck near the police headquarters and a nearby fuel facility in the center part of Tikrit, some 170 km north of the Iraqi capital of Baghdad, the source said.
The guards of the headquarters may not have suspected the tanker truck because fuel tanker trucks are commonly seen entering the fuel facility to deliver gas and oil for the provincial government, he said.
Earlier, the police put the toll at 10 killed and 30 wounded by the blast, which destroyed parts of the two buildings and set a huge fire to the fuel facility.
Iraqi security forces cordoned off the scene and blocked all roads leading to the city center, and ambulances and police vehicles evacuated the victims to local hospitals and medical centers.
No one has so far claimed responsibility for the attack. However, al-Qaida front in Iraq is usually responsible for the most deadly attacks in the country, raising fears that the terrorist group may stage a comeback taking advantage of possible spillover from the ongoing conflict in neighboring Syria.
Violence and high-profile bomb attacks are still common in Iraqi cities despite a dramatic decrease since its peak in 2006 and 2007, when the country was engulfed in sectarian killings.