Regierungsbezirk Zichenau was a Regierungsbezirk, or administrative region, of the Nazi German Province of East Prussia in 1939–45, established in German-occupied Polish territory during World War II. The regional capital was Zichenau (Ciechanów).[1] It was also referred to under the designation of South East Prussia (German: Südostpreußen) which, however, was later sometimes also applied to Bialystok District, although the latter was not incorporated into, but merely attached to East Prussia.