Russian President Vladimir Putin, centre, attends a meeting at the headquarters of the group of troops Dnepr in the Kherson direction, at an undisclosed location, Ukraine. (AP)
Russian lawmakers this week toughened penalties for "terrorism" and sabotage as Moscow pursues its military offensive against Ukraine.
The FSB in the city of Kerch "prevented the preparation of sabotage at a facility of the energy system of the peninsula," annexed from Ukraine in 2014, it said in a statement.
"A citizen of Russia and Ukraine, born in 1971, who was involved in the preparation of this crime, was detained," the statement said.
According to the FSB, the suspect was being held for planning to commit "sabotage" and "possession of explosives or explosive devices".
The charges carry a possible life sentence, the FSB said.
It also said the suspect was in contact "with a representative of Ukraine's security services, who coordinated his criminal activities".
FSB chief Alexander Bortnikov this month accused Ukraine and Western powers of inciting Russians to armed rebellion.
President Vladimir Putin also accused Western security services of being involved in "terrorist" attacks in Russia.
In early April, Russia detained a young woman after an explosion killed a top military blogger in Saint Petersburg, blaming Ukraine and the opposition.