Europe is "the next target of Russia," NATO Secretary General Mark Rutte said on Thursday during a speech in Berlin.
The former Dutch Prime Minister again called on the military alliance's member states to step up their defence investments.
Rutte said the alliance must prevent a war before it begins, stressing that this requires a clear understanding of the threat.
"But for that, we must be fully aware of the danger," he said, noting that many countries still lack a genuine sense of urgency regarding the conflict with Russia.
He once again urged allies to increase their national defence budgets and provide greater support to Ukraine.
He warned that a Ukrainian defeat would cost the European continent hundreds of billions of euros.
