The prosecutor at the International Criminal Court, Fatou Bensouda, said Tuesday that she had reopened a preliminary war crimes investigation into accusations that British officials were responsible for the systematic abuse of Iraqi prisoners by Britain’s military from 2003 to 2008. A similar investigation was closed in 2006, but Ms. Bensouda said she would review whether new information she received in January justified reopening the case. Although Iraq has not signed the Rome Statute, which governs the court’s proceedings, Britain has, and its citizens can in theory be prosecuted for crimes committed in Iraq or elsewhere. However, the court, which is based in The Hague, can proceed only if the allegations are not being properly investigated by the British authorities themselves.