Diyala provincial council spokeswoman Samira al-Shibli said emergency workers were still frantically trying to rescue victims from beneath the rubble several hours later.
Diyala health directorate spokesman Faris al-Azawi said the bomber drove his car past a security gate and detonated his explosives right outside the headquarters of an army intelligence battalion in Kanan, east of the provincial capital of Baqouba, 35 miles (60 kilometers) northeast of Baghdad.
An army commander in Diyala described a horrific scene of the building collapsing on soldiers inside. He said the bomber drove his car up through a back gate and through a yard to get to the headquarters.
The commander spoke on condition of anonymity because he was not authorized to brief the media. He said dozens of soldiers were killed or wounded.
Al-Azawi said 10 soldiers were killed. He said at least 29 people also were wounded, including 14 soldiers.
Al-Shibli, the council spokeswoman, said a second bomb was discovered nearby but diffused by officials before it could explode. She said the first blast may have been from a bomb in a parked car. Conflicting information is common in the immediate hours after an attack.
A senior Iraqi intelligence official in Baghdad blamed the attack on al-Qaida and said authorities believe the same cell of insurgents may also be plotting a similar strike against security forces in the capital.
He said al-Qaida suspects being held in prison have tipped off authorities to the upcoming threat, and said insurgents have already planned a strike in Baghdad but need funding to carry it out.
The intelligence official spoke on condition of anonymity because he was not authorized to brief the media.
In January, the Islamic State of Iraq, an al-Qaida front group, has claimed responsibility for two bombings at security force headquarters in Baqouba that together killed 10 people.
Also Monday, a local lawmaker in the central Salahuddin province said one inmate was killed the day before by jumping off the roof in an effort to escape from prison during a riot.
Provincial council member Abdullah Jabara said 22 people, including 15 guards, were injured in the melee that started after officials found holes in the prison's steel fence and discovered an escape plan by inmates linked to al-Qaida.
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Lara Jakes in Baghdad and Sameer N. Yacoub in Amman, Jordan, contributed to this report.
