"Divisions and units of the Ukrainian armed forces which are stationed in the vicinity of the administrative border with Crimea are on high alert. A build-up of corresponding groups has been carried out," Viktor Muzhenko said on his Facebook page.
The move comes a day after the Russian Federal Security Service said it had foiled terrorist attacks in Crimea organized by the Ukrainian main intelligence directorate, and stamped out a spy ring detaining both Russian and Ukrainian nationals involved in the plot. Two Russian officers were killed.
Crimea rejoined Russia after a 2014 referendum in which over 96 percent of the Crimean population voted in favor of reunification. Sevastopol, which has a federal city status, supported the move by 95.6 percent of the votes.