Russian President Vladimir Putin has held a meeting of the country's top brass to discuss boosting security in Crimea after reports of foiled attacks.
Intelligence chiefs said two people were killed fending off what they described as a series of attempted attacks in Crimea by Ukrainian "saboteurs".
Ukraine rejected the claims as "fantasy" and "a provocation".
Russia annexed the Black Sea peninsula in March 2014 following a hastily called referendum, an event that sparked Russian-backed separatists to begin fighting in eastern Ukraine, where deadly fighting is continuing.
The Kremlin said Mr Putin had chaired a Security Council session to discuss "additional measures" to ensure security at Crimea's de-facto border, the territorial waters around it and Crimean air space.