Russia's Federal Security Service (FSB) says it has detained a senior reconnaissance officer from a Ukrainian military unit and claims he was planning acts of sabotage in Crimea.
The FSB said on August 15 that Hennadiy Limeshko was detained on August 12 while attempting to disrupt power lines on the Russian-controlled peninsula. He was placed under pretrial arrest.
According to the FSB, the suspect had explosive devices in his possession.
A spokesman for Ukraine's armed forces, Yuzef Venskovych, said on August 15 that Limeshko is not an active-duty serviceman.
Limeshko served in the Ukrainian Army between November 2016 and May 2017, Venskovych said, adding: "He was discharged in May this year due to incompatibility with service."
The announcement came days after a Russian court sentenced two Ukrainian nationals in separate cases to lengthy prison terms on terrorism charges.
Rights activists say Russia has jailed several Ukrainians on trumped-up, politically motivated charges since Moscow seized Ukraine's Crimea region in March 2014.
In March, the European Parliament called on Russia to free more than 30 Ukrainian citizens who are in prison or who have had their freedom of movement restricted in Russia, Crimea, and parts of eastern Ukraine that are controlled by Russia-backed separatists.
With reporting by Unian, RIA Novosti and Interfax