MOSCOW (AP) — Russia's main security agency said Thursday that it has arrested 25 Ukrainian citizens on suspicion of planning sabotage in Russia.

The Federal Security Service, the main KGB successor agency, said in a statement carried by the state RIA Novosti news agency that the suspects were planning to conduct sabotage and terror attacks in seven regions across Russia last month. It didn't say when they were arrested or give any further details.

NTV television reported Thursday those arrested included three activists from Right Sector, a Ukrainian nationalist group that played a role in the ouster of Ukraine's pro-Russian President Viktor Yanukovych in February. The report included footage of three suspects in custody.

NTV also reported the suspects had instructions from Ukraine's Security Service to take pictures of Russian military's movements on the border with Ukraine and establish contact with Russian radical groups.

Russia has deployed up to 40,000 troops along the border with neighboring Ukraine, according to NATO, raising fears of another possible invasion following the Russian annexation of Ukraine's Crimean Peninsula.