In the declaration on Tuesday, NATO and the EU stated: "Today, we are faced with the gravest threat to Euro-Atlantic security in decades. Russia's brutal war on Ukraine violates international law and the principles of the U.N. Charter."
They pledged to "take our partnership to the next level" in response to the growing threats and challenges.
Russian Foreign Ministry spokeswoman Maria Zakharova said the move "confirms the complete subordination of the European Union to the tasks of the North Atlantic bloc, which is an instrument to guarantee U.S. interests by force".
She said the Europeans faced "the unenviable fate of an American vassal, losing their positions in world politics and economics, falling into increasing dependence on Washington with every step".
The statement was in line with Moscow's efforts to cast the war in Ukraine as part of an existential struggle with Western nations it says are bent on Russia's destruction.
Faced with unprecedented Western sanctions, President Vladimir Putin has said Russia will step up cooperation with other partners, notably China, in order to counter U.S. hegemony and forge what he calls a "multipolar world".
The United States and its allies have condemned Russia's invasion of Ukraine as an imperial land grab, while Ukraine has vowed to fight until the last Russian soldier is ejected from its territory.
The United States has denied Moscow's claims that it wants to destroy Russia, and President Joe Biden has cautioned that a conflict between Russia and NATO could trigger World War Three.
(Reporting by Reuters; Editing by Gareth Jones)
