Pro-Russian insurgents dug in April 15 across eastern Ukraine, fortifying positions around seized buildings and erecting new barricades even as Ukrainian troops and tanks set up outside one eastern city now controlled by armed men. In Kyiv, Ukraine's acting president, Oleksandr Turchynov, announced an "anti-terrorist operation" to root out the separatists, but it was unclear how that measure differed from the one announced April 14, which resulted in no visible action.