The head of NATO capped off a trip to Japan with a call for more support for Ukraine. It has been almost a year since Russia invaded. Jens Stoltenberg says the outcome of the conflict could challenge stability and security in Europe and beyond.

"If Putin wins, the message to Moscow and to Beijing would be that they can achieve what they want through use of brutal force," Stoltenberg said in a speech at a Tokyo university.

That force is on display in the eastern region of Donetsk. Fighting between Russian and Ukrainian forces remains fierce. Officials in Kyiv say Moscow could launch another major offensive in the coming weeks.

In an interview with NHK, the NATO chief said international support was not just about Ukraine keeping the invasion at bay.

He said, "It's extremely important that we deliver weapons, ammunition, military support to ensure that Ukraine is able to liberate to retake territory and to push back the Russian invaders and win and prevail as a sovereign independent nation in Europe."

Western nations have already pledged as many as 140 modern battle tanks to bolster defenses. But Ukraine says it needs fighter jets to fight back.

Stoltenberg would not comment on what kinds of weapons would be delivered next.

"There's ongoing consultation process among NATO allies and partners and also of course with Ukraine. And the type of weapons systems we are delivering has evolved over, over the year, as the war has evolved," Stoltenberg said.

But Ukraine's calls for modern fighter jets are so far going unanswered. The US has already said it would not provide Ukraine's air force with deliveries of the American F-16 aircraft.