A Ukrainian government official has been detained on charges of spying for Russia, Ukraine's security agency said Thursday.
Ukraine's Security Service, or SBU, said the suspect allegedly passed government secrets to his Russian handlers. Ukrainian media reports identified the suspect as an aide to Prime Minister Volodymyr Groysman who accompanied him on foreign trips.
Groysman thanked the SBU for its "vigilance and professionalism" on Facebook.
British Prime Minister Theresa May said on a trip to Warsaw that she is aware of reports that an interpreter for Ukraine's premier who was photographed with her in Downing Street has been arrested on suspicion of being a Russian spy.
She added that "the action that's been taken is a matter for the Ukrainian authorities."
Yezhov was detained at his workplace Wednesday evening, and Ukrainian television stations have broadcast footage of him being taken away in handcuffs escorted by SBU agents.
On Thursday, the SBU announced that one of its senior officers was also detained on charges of spying for Russia.
Russia and Ukraine have been in a tug-of-war following Moscow's 2014 annexation of Crimea and support for pro-Russia insurgency in eastern Ukraine.