The trial has opened in Sevastopol of two Ukrainian nationals, Volodymyr Dudka and Oleksiy Bessarabov, who are charged with plotting sabotage in Russia-annexed Crimea.
The defendants' lawyer, Sergei Legostov, told RFE/RL that the trial started on August 2 and is being held behind closed doors.
Dudka, Bessarabov, and a third Ukrainian man, Dmytro Shtyblykov, were arrested in Crimea in November 2016 and charged with attempted sabotage.
At the time of the arrests, Russia's Federal Security Service (FSB) accused the three of being members of a Ukrainian "saboteur group from the main intelligence directorate of the Ukrainian Defense Ministry."
Ukraine's Defense Ministry rejected the FSB's allegations, calling them "another fabrication of the Russian secret services aimed at justifying its own repressive measures against local residents and discrediting Ukraine in the international arena."
Shtyblykov was tried separately. In November, the Sevastopol City Court found him guilty of attempted sabotage and illegally possessing weapons and sentenced him to five years in prison.
Rights activists say Russia has jailed several Ukrainians on politically motivated charges since Russian military forces occupied Crimea in early 2014 and, less than a month later, annexed the territory from Ukraine after a referendum widely condemned as illegitimate.