Russia's FSB has detained another citizen of Ukraine / Photo from

Russia's Federal Security Service (FSB) has reported that a Ukrainian national who was allegedly involved in preparing terrorist attacks and tried to recruit Russian citizens has been detained in Russia-occupied Crimea.

Russian counterintelligence agents "put an end to activities of the Main Intelligence Directorate of Ukraine's Defense Ministry, aimed at organizing and committing acts of terrorism, recruiting citizens and stealing information containing state secrets," the FSB said on its website.

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They claim "terrorists" are chief of a Ukrainian military intelligence unit, stationed in the city of Kherson, Colonel Oleh Akhmedov, as well as other persons whom he had allegedly recruited.

"The group included a female military officer of the Armed Forces of Russia, who is suspected of sharing state secrets in 2017-2018, and a citizen of Ukraine who is suspected of espionage on the orders of Ukrainian special services," the FSB said.

The Russians also reported that criminal cases were opened against the detainees on charges of high treason and espionage. The detained woman, who is a citizen of Russia, is under house arrest because she has a child, while the Ukrainian has been remanded in custody. The local media published footage of their detention.

According to Radio Free Europe / Radio Liberty (RFE/RL), the alleged espionage activity was uncovered during a separate investigation opened in January against another Russian suspect accused of building weapons caches in Crimea on the orders of Akhmedov.

"The timing of the announcement has raised eyebrows, as it comes a day after the Ukrainian Security Service (SBU) said one of the country's top officials had been detained on suspicion of collaborating with the FSB," RFE/RL said. "The SBU said Major General Valeriy Shaitanov was suspected of high treason and terrorism for working for the FSB in 2014 and had planned 'terrorist acts' in Ukraine."