Scholz insisted at the end of a NATO summit in Madrid that the Western military alliance was "not a threat to anyone" and said it was Putin "who has made imperialism the goal of his politics".

Putin on Wednesday hit out at NATO after its leaders dubbed Moscow their "most significant and direct threat" following the Kremlin's of invasion of Ukraine.

"The NATO countries' leaders wish to... assert their supremacy, their imperial ambitions," he said.

The Ukraine war has also pushed NATO to launch the largest overhaul of its defence and deterrence capabilities since the end of the Cold War.

Moscow's invasion has pushed Finland and Sweden to apply to join the alliance, which would more than double NATO's border with Russia.

NATO chief Jens Stoltenberg said that the alliance was "prepared for all eventualities" if Moscow reacted to Finland and Sweden joining.

"We are there to protect all allies and of course also Finland and Sweden," he said.

NATO countries have funnelled billions of dollars of arms to Ukraine to help it fight off Russia's aggression.

Stoltenberg said the alliance was committed "to make sure that Ukraine prevails as an independent sovereign state in Europe".

"President Putin's brutal war against Ukraine is absolutely unacceptable. It's causing a lot of death and damage for Ukrainian people, but it also has ramifications over the whole world," he said.

"It's President Putin that should withdraw his forces and end this war immediately by stopping attacking a democratic sovereign nation and causing so much suffering in Ukraine."