Japan has been quick to join the US-led economic sanctions against Russia's war on Ukraine and provide humanitarian aid and non-combative defence equipment to Ukrainians.

Japanese Prime Minister Fumio Kishida has highlighted his concern that Russia's aggression in Europe could happen in Asia, where worries are growing over an already assertive China and its escalating tension near Taiwan.

Japan has also significantly stepped up its ties with NATO recently.

“The war in Ukraine also demonstrates that our security is closely interconnected,” Stoltenberg said during his visit at the Iruma Air Base north of Tokyo, where he started his Japan visit on Tuesday after arriving late Monday from South Korea.

“If President Putin wins in Ukraine it will be a tragedy for the Ukrainians, but it will also send a very dangerous message to authoritarian leaders all over the world because then the message will be that when they use military force they can achieve their goals,” he said.

“So the war in Ukraine matters for all of us."

Stoltenberg said his visit to Japan “is a way to further strengthen the partnership between NATO and our highly valued partner Japan.”

He is set to meet with Kishida and hold a joint news conference later Tuesday.

Japan, already a close ally of the United States, has in recent years expanded its military ties with other Indo-Pacific nations as well as with Britain, Europe and NATO amid growing security threat from China and North Korea.

Japan issued a new national security strategy in December stating its determination to build up its military and deploy long-range missiles to preempt enemy attacks in a major break from its post-World War II principle that limited itself to self-defense.

Japan also hopes to further ease restrictions on arms export to strengthen the country's defence industry.

While in South Korea on Monday, Stoltenberg called for Seoul to provide direct military support to Ukraine to help Kyiv to fight off the prolonged Russian invasion.

So far, Seoul has only provided humanitarian aid and other support, citing a long-standing policy of not supplying weapons to countries in conflict.

Stoltenberg also met with South Korean President Yoon Suk Yeol on Monday and discussed Seoul's commitment to support Ukraine and NATO’s possible role in dissuading North Korea from its growing nuclear ambitions following an unprecedented number of ballistic missile tests in 2022, Yoon’s office said.

Stoltenberg on Sunday mentioned US intelligence reports accusing North Korea of providing weapons to Russia to support its war in Ukraine.

North Korea condemned his visits to South Korea and Japan, saying that NATO was trying to put its “military boots in the region” and attempting to pressure America’s Asian allies into providing weapons to Ukraine.

In a statement released by the state-run Korean Central News Agency, North Korea criticized increasing cooperation between NATO and U.S. allies in Asia as a process to create an “Asian version of NATO” that would raise tensions in the region.