Nikolai Iyochenko, who started his undercover duty at the USSR Embassy in Ankara on 26 January 1956 under the  cover  of an assistant military attaché and carried out spying activities against Türkiye,  was caught red-handed in an operation on 10 May 1956. The declaration of Iyochenko as persona non grata and subsequent events delivered a heavy blow on the activities of the USSR’s military intelligence service GRU in Türkiye.