Crimean Tatar activists have reported armed checkpoints being erected at scattered sites around the Russian-occupied peninsula, and unusually large concentrations of Russian hardware in northern regions.
Ukraine's border guard service, meanwhile, reported that Russian authorities had blocked all road entry to the Black Sea peninsula for several hours on August 7.
Nariman Celal, a top official with the executive body of the peninsula’s Crimean Tatar minority, reported tanks and other heavy weaponry concentrated around two key northern settlements, near the administrative border with the Ukrainian mainland.
The Crimean Human Rights Group, a local nongovernmental organization, said it had also received reports, photographs, and videos from witnesses showing Russian military trucks being transported on trains on August 6 near Kerch, an eastern port town that is opposite Russia's Stavropol territory.
Rafat Chubarov, a member of Ukraine’s parliament and one of the Crimean Tatar community's most prominent figures, told the news portal 112.ua that the Russian maneuvers appeared to be a training exercise.
Russia seized Crimea in the aftermath of the so-called Euromaidan protests in Kyiv that forced President Viktor Yanukovych to flee.
Moscow later declared it had annexed the peninsula, a move that has been rejected across the globe. Its naval base at Sevastopol is the home for the Russian Black Sea fleet.
With reporting by RFE/RL’s Krym.Realii project, 112.ua and Interfax