Russia's Federal Security Service (FSB) says it has apprehended three Ukrainian nationals suspected of working for Ukraine's intelligence agencies, a claim Kyiv immediately rejected.
In a statement on December 2, the FSB identified two of those detained in Russia as Ukrainian nationals Zinoviy Koval and his son Ihor, who allegedly collected classified information for Ukraine's domestic intelligence agency, the SBU.
The statement identified the third Ukrainian man detained in Russia as Oleksandr Tsylyk from the Kyiv region.
Tsylyk allegedly confessed he was an agent of Ukraine's GRU military intelligence, and that he planned to commit a "terrorist act" on Russian territory using explosives.
The statement did not say when and where exactly the alleged spies had been detained.
The SBU denied the allegation, with spokesman Artem Dekhtyarenko saying that "such FSB statements should be looked at through the prism of the hybrid war, in which information propaganda and distribution of fake news have a significant role."
Last month, a Russian court sentenced an alleged GRU agent, Serhiy Shvydenko, to 6 1/2 years in prison on charges of coordinating and supervising activities of a sabotage group in the Russian-occupied Crimea region, the FSB said in a separate statement.
Ukrainian officials did not immediately comment on the FSB allegations.
Kyiv and rights activists say Russia has jailed several Ukrainians on trumped-up, politically motivated charges since Moscow seized Crimea in 2014 and threw its support behind armed separatists in eastern Ukraine, where more than 13,200 people have been killed in the ongoing conflict.