At an informal meeting in Oslo, the NATO Secretary General also touched on how to iron out Sweden's accession process to joining the bloc.
ADVERTISEMENTNATO chief Jens Stoltenberg said Thursday in Oslo that "NATO's door is open" for Ukraine to join the alliance, and Russia does not have "a veto against NATO enlargement."
Stoltenberg made the comments at an informal NATO meeting held in the Norwegian capital.
When asked about missile attacks in Kyiv, Stoltenberg called attacks on Ukrainian civilians "a war crime" and compared it to the 22 July 2011 Norway terrorist attacks.
The NATO Secretary General also recalled the commitments and actions already undertaken by Kyiv's allies, particularly in military terms, stressing that it is necessary to create a framework of security guarantees to prevent history from repeating itself.
“We don’t know when the war ends but we must ensure that when it does we have credible arrangements in place to guarantee Ukraine’s security in the future and to break Russia’s cycle of aggression," Stoltenberg said.
"If President Putin wins in Ukraine it will make the world more dangerous, it would send a message that when authoritarian leaders use military force they get what they want. And that will also make us more vulnerable.”
"Those responsible for war crimes in Ukraine must be held accountable," he said.
Separately, he reiterated that Turkey and all other NATO members invited Sweden to become a full NATO member and that NATO is working to make it happen "as early as as possible."
Commenting on the situation in Kosovo, he said violence against NATO peacekeepers is unprovoked and unacceptable.
"To ensure that we have the forces we need at any time, we have decided to deploy our operational reserve," he added.
NATO members will formally convene at a summit in Lithuania in July, where they hope to overcome Sweden's accession to the bloc.