WASHINGTON—The Justice Department is creating a new office of attorneys tasked with stripping citizenship from immigrants who obtained it illegally by lying or omitting information on their applications.

The new denaturalization section, to be housed within the Office of Immigration Litigation, will sue to strip U.S. citizenship from “terrorists, war criminals, sex offenders, and other fraudsters,” the department said on Wednesday. It will target individuals who have obtained citizenship “by concealment of a material fact...