The prisoners had lured a guard into their cell while his comrades were sleeping, claiming an inmate there was critically ill. They then stabbed him to death, two senior security officials said.
Jailbreaks are frequent in Iraq and, as with other security breaches, they have cast doubts on the ability of the authorities to secure the country, mired in sectarian tensions.
Also Friday, a car bomb went off near a security checkpoint in the western city of Ramadi, killing five policemen and wounding seven others, said police officials.
In a drive-by shooting in western Baghdad, gunmen shot and killed two government employees in their car. And police said a bomb exploded near an out-door market in Madain area, just south of Baghdad, killing one person and wounding four.
A car bomb exploded inside a fish market in Baghdad's southeastern Shiite-majority suburb of Nahrwan, killing four and wounding 14, police said.
In the western city if Ramadi, a car bomb went off near a security checkpoint, killing five policemen and wounding seven others, said police officials
At night, six people were killed and 18 others were wounded in a car bomb explosion in a commercial street in a town, just south of Baghdad.
Medics in nearby hospitals confirmed the casualty figures for all the attacks. All officials spoke on condition of anonymity because they were not authorized to talk to media.
Deadly insurgent attacks have been on the rise since a security crackdown on a Sunni protest camp in a northern town last April.
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Associated Press writer Qassim Abdul-Zahra contributed to this report.