NATO said on Friday that Russian President Vladimir Putin’s warnings to its members were "unacceptable and counterproductive".
Russia said Thursday it would consider any nuclear aggression against it or its allies as a nuclear attack.
Addressing the Russian Federal Assembly, Putin said the response to such an attack would be immediate, adding that the country was capable of deterring such a threat and possessed modern weapons.
"Russian statements threatening to target allies are unacceptable and counterproductive," NATO spokeswoman Oana Lungescu said in a statement.
"As we have repeatedly made clear, the Alliance’s missile defence is neither designed nor directed against Russia. Our system defends against ballistic missiles from outside the Euro-Atlantic area," Lungescu said.
Stating that they did not want a new Cold War or arms race, Lungescu said NATO was a defensive alliance, which stood ready to defend all members against any threat.
"All Allies support arms control agreements which build trust and confidence, for everyone's benefit. We continue to work for more military predictability and transparency, including in the NATO-Russia Council," she said.
Noting "Russia's aggressive actions in Ukraine, and its continued military build-up from the Barents Sea to the Mediterranean," Lungescu said NATO was pursuing a "twin-track approach" to Russia in response, which she said included "strong deterrence and defense, combined with meaningful dialogue".
"We are committed to delivering on both tracks," she underlined.