"[The FSB] supressed illegal activities of the former employees of an organization of the defense industry complex — Russian citizens, agents of the Main Directorate of Intelligence of the Ukrainian Defense Ministry, who are suspected of ... preparing to commit bomb attacks ... at railway tracks in the Kursk and Belgorod regions, which are used for supply of Russian armed forces' units participating in a special military operation in Ukraine," the FSB said in a statement.
As a result of search operations, FSB officers have seized a plastic explosive weighing 4 kilograms (8.8 pounds), four fuses, design documentation and military items, as well as $150,000.
"The suspects are in custody and are confessing," the statement read.
A criminal case has been initiated under articles on high treason and preparation for sabotage, the FSB added.