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NATO's Secretary-General Jens Stoltenberg told CNBC it would be a "tragedy" for Ukrainians if Russian President Vladimir Putin wins the war.

Victory would also send a dangerous message to other authoritarian leaders, he warned.

Speaking as NATO foreign ministers meet on Monday to discuss developments in the war and what further support Ukraine needs, Stoltenberg said it would "be a tragedy for Ukrainians if President Putin wins but also dangerous for us."

"The message sent to authoritarian leaders, in Moscow but also in Beijing, would be that when they use military force and invade another country, they get what they want. Therefore we will be more vulnerable if President Putin wins so it's in our security interests to support Ukraine," he told CNBC's Silvia Amaro in Brussels.

Concerns have grown recently that public support for continued military funding for Ukraine has declined. Political shifts in Europe have also heralded new leadership in a number of countries that is more skeptical about continued support for Kyiv.

Stoltenberg said bipartisan support for Ukraine remained strong in the U.S., despite some rumblings of Republican discontent over military aid. The U.S. has committed around $44.2 billion in security assistance to Ukraine since the beginning of Russia's unprovoked invasion in February 2022.

"I'm absolutely confident that the United States understands that it's dangerous for the United States if President Putin wins in Ukraine," he said.

— Holly Ellyatt