Ukraine does not deny nor confirm. Do you understand? "Does not deny nor confirm". And if you ask US intelligence services if they are helping... they "not deny nor confirm".
Now repeat with me once more: "I am safe in Putin's Russia, I am safe in Putin's Russia, I am safe in Putin's Russia..."
I understand it. When there is confirmation from the Ukrainian side, then it will be appropriate to talk about it here. For now, I can only say that even terrorists act more honestly than Ukraine, because usually some specific terrorist organization takes responsibility for the strike. There is no responsibility - it means that until the end of the investigation it is just an accident.