Iraq says it will vigorously pursue court action against five security guards from the American company Blackwater, who are accused of killing 17 unarmed civilians in Baghdad two years ago.
A government spokesperson called a decision by a federal judge in the United States to dismiss charges against the men "unacceptable" and "unfair".
He said Iraqi investigations had confirmed unequivocally that the guards committed a crime on 16 September, 2007.
The five all pleaded not guilty to manslaughter. A sixth guard admitted killing at least one Iraqi. Lawyers for the five guards say they were acting in self-defence.
The BBC reports the judge dismissed the charges against the guards over procedural errors.
District Judge Ricardo Urbina said the Justice Department used evidence that prosecutors were not supposed to have.