The blast came a day after suicide bombers killed 27 people in attacks in two Iraqi cities. The three bombs have shattered the lull that followed the poll.
The al-Qa'ida wing in Iraq, led by the Jordanian militant Abu Musab al- Zarqawi, claimed responsibility for the latest attack, as it did for Monday's blasts in Mosul and Baquba.
"Here come the convoys of martyrs to strike the headquarters of infidels and apostates, and this is the beginning of the escalation we had promised," the group said in an internet statement. It described the victims as "apostate pagan guards who are agents of the Jews and crusaders". Police said the attacker's target was a truck carrying recruits into the base in a disused airport. The US military said the bomber was believed to have been on foot.
Iraq's security forces have borne the brunt of insurgents' attacks. The US military is trying to build them into a force capable of defeating the militants.
Elsewhere in Baghdad, a bomb outside a popular restaurant killed one Iraqi, and gunmen ambushed a politician's convoy, killing two of his sons. Mithal al-Alusi, who has been a critic of Syria and Iran and was criticised in Iraq for visiting Israel last year, survived. Three Iraqi soldiers and two insurgents were also killed in a firefight south of Baghdad and in Samarra, north of the capital, an Iraqi civilian was killed.
Iraqi police claimed at least one success, arresting a man they believe was involved in the beheadings in Mosul. The government also said it captured Basher Mutar al-Tikriti, a relative of Saddam Hussein, last month. (Reuters)