I have no doubt that it was done by helicopters, I was just suspicious to the statement "nobody got a good look" or some form of awareness of a border crossing by the enemy. Still, like I said, it could be by Putin's creations and Ukraine is denying it. But again, there are no rules being followed in this deadly game. Only the "fog of war".
Kleptocrats: a ruler who uses political power to steal his or her country's resources.
Kleptocracy: government by those who seek chiefly status and personal gain at the expense of the governed.