Russia, which annexed Crimea from Ukraine in 2014, said this week it had foiled a Ukrainian sabotage mission.
It accused the Ukrainian government in Kiev of trying to send saboteurs into Crimea and reported the deaths of a soldier and a secret police officer in an operation to foil the alleged plot.
The Russian military has announced on the 12th of August the delivery of new air defence missiles to Crimea, in a move scheduled before the latest tension with Ukraine.
The S-400 Triumph missile systems were earmarked for troops in Crimea last month, Russian media said at the time.
Moscow also announced exercises in Crimea next week to simulate an attack by weapons of mass destruction (WMD).