A group of prisoners attempted to escape after storming the prison armory, the U.S. military said in a statement.
In other developments today, the United Nations' adviser to Iraq's electoral officials, Craig Jenness, rejected calls for a re-run of the 15 December polls.
"The United Nations is of the view that these elections [in Iraq] were transparent and credible. Turnout was high, the day was largely peaceful, all communities participated," he said.
Thousands of people backing Sunni Arab and secular Shi'ite politicians have protested for days over alleged vote fraud and called for a new vote.
Partial vote counts show Shi'ite and Kurdish blocs with a large lead. The Iraqi election commission's head, Hussein Hindawi, warned today that the fraud accusations are endangering the lives of the panel's members and encouraging insurgents to attack them.
The official election results are expected to be announced shortly after the New Year.