The embassy says it is waiting for official notification from Moscow of the reason for the entry ban.
Ukrainian media reported on Tuesday that the country's Foreign Ministry sent an official note to Russia requesting an explanation for the refusal of entry.
"We received the note yesterday and immediately contacted the relevant official bodies [in Moscow]. We are waiting for a reply and believe that we will get it soon," Council Ambassador Vsevolod Loskutov said.
Ukrainian newspaper Den says Hryenko departed for Russia on April 24 to report on a memorial rally at the Mitino cemetery near Moscow dedicated to the Chernobyl nuclear power plant tragedy.
Border guards at the Suzemka railway station denied him further travel, explaining that Hryenko was on a persona-non-grata list.
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