Crimea has been left without power after several pylons supplying electricity from the Ukraine were "blown up" up overnight.
Four power lines were reportedly toppled, leaving two million inhabitants on the disputed Crimean peninsula without electricity.
Russia has declared a state of emergency in Crimea until power is fully restored, news agency RIA reported.
It was not immediately clear who had damaged the pylons, but a Russian senator described the move as an "act of terrorism" and implied that Ukrainian nationalists were to blame.
Ukrainian authorities have said activists tried to block efforts to repair the pylon, and that the damage seen is likely a result of shelling of explosive devices.