An alleged Al-Qaeda fighter being transferred out of a Baghdad prison on Thursday seized a guard's gun and killed two security members and wounded another before shooting himself, officials said.
The prisoner was being taken to court to face trial from Tasfirat prison in the centre of the capital.
A small riot broke out at the facility two days ago before being put down without any fatalities.
On Thursday the inmate managed to grab a weapon from a nearby guard and opened fire, a justice ministry official said, speaking on condition of anonymity.
The prisoner killed two security force members - a police major and a prison guard - and wounded one other before taking his own life, the official added.
An interior ministry official and a medical source confirmed the incident and the toll.
The incident was reminiscent of a similar, but deadlier, prison shooting in May 2011, when an accused Al-Qaeda leader overpowered a policeman and sparked a jail mutiny that led to the deaths of six Iraqi police and 11 inmates.
At that time, the prisoner overpowered the police lieutenant leading him to an interrogation, taking his weapon and shooting him dead.
The inmate, who was allegedly the chief of Al-Qaeda's front group in Baghdad, then freed several other prisoners, with the group proceeding to kill several officers before attempting to flee.
They were all eventually killed. Jailbreaks and prison unrest are relatively common in Iraq. In March, 19 inmates escaped from a prison in the northern city of Kirkuk, and in January, 11 prisoners tunnelled out of a prison in the northern Kurdish province of Dohuk.