Ukrainian media reports identified Yezhov as a senior aide and personal interpreter to Prime Minister Volodymyr Groysman.
The SBU said in a statement late on Wednesday the suspect "gathered information about government activities with special equipment" and passed it to his handlers.
A Ukrainian government official has been detained on charges of spying for Russia, Ukraine's security agency said Thursday.
However, Moscow announced that it was recalling its officers, claiming that their Ukrainian counterparts were obstructing their work and blocking access to the front lines.
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As the gushing narrator says, these holiday charmers will leave you asking, "Wait, how do I know that actor?" In another "movie", Bearstick plays a mysterious royal who turns out to be, gasp, Prince Santa .
Prior to his work in the cabinet of ministers, Yezhov worked in the presidential administration, translating during press-conferences with former president Viktor Yanukovych during visits by foreign leaders.
Aide to the Ukraine interior minister, Anton Gerashchenko, said Yezhov was recruited when he was working at Ukraine's embassy in Washington and acted in Russia's interests for at least two years.
Although the Russia-backed insurgency in Ukraine has seen 10 different truce deals since it began in April 2014, both sides have accused the other of breaking the agreements nearly instantly.
The two countries became arch-foes following the subsequent annexation by Moscow of Ukraine's Crimean peninsula and the ongoing conflict in eastern Ukraine, where pro-Russian separatists have declared independence. The last ceasefire came into effect in August, and Russian officials from the Joint Center for Control and Coordination (JCCC) in Ukraine had been part of a team observing the peace.
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