The reaction of Alexander Zakharchenko was reasoned and tough (quote DAN):
The statements of Poroshenko and his representative at the Minsk talks of Kuchma about the need for Ukraine to join NATO are aimed at the destruction of the Minsk agreements. If Ukraine begins to prepare a referendum on joining NATO or other procedures, the DNR will immediately withdraw from the Minsk agreements and begin clearing the entire territory of Donbass from Kiev occupation. I am sure that many other regions of Ukraine in this case will leave its composition.
By the way, another “sequence” of Poroshenko’s statements attracts attention. A couple of days ago, the President of Ukraine said that Ukraine was not ready to become a member of the North Atlantic Alliance, and the Alliance was not ready to accept Ukraine, but now he said: "Ukraine has matured to join NATO."