South Korean President Yoon Suk Yeol, center right, talks with NATO Secretary-General Jens Stoltenberg during a meeting at the presidential office in Seoul, South Korea, Monday, Jan. 30, 2023. AP
Stoltenberg is in Seoul on the first leg of his Asia trip, which will also take in Japan, as part of a drive to boost ties with the region's democratic allies in the face of the Ukraine conflict and growing competition from China.
He met top South Korean officials Sunday, and on Monday urged Seoul to do more to help Kyiv, saying there was an "urgent need for more ammunition".
He pointed to countries like Germany and Norway that had "long-standing policies not to export weapons to countries in conflict" which they revised after Russian President Vladimir Putin invaded Ukraine in February last year.
"If we believe in freedom, democracy, if we don't want autocracy and tyranny to win then they need weapons," he said, speaking at the Chey Institute in Seoul.
South Korea is an increasingly important arms exporter globally and has recently signed deals to sell hundreds of tanks to European countries, including NATO-member Poland.
But South Korean law bans the export of weapons to countries in active conflict, which Seoul has said makes it difficult to provide arms directly to Kyiv, although it has provided non-lethal and humanitarian assistance.
South Korea opened its first diplomatic mission to NATO last year.
Stoltenberg said it was "extremely important that President Putin doesn't win this war", saying it would make the world a more dangerous place.
"Because then the message to authoritarian leaders, also in this part of the world, in Beijing, will be that the use of force is the way to get what you want," he said.
He said that NATO did not regard China as "an adversary" and believed in engagement on issues from arms control to climate change.
NATO allies still trade with China, he said, but added the recent lessons from Europe's vulnerabilities on Russian gas were a key lesson on not becoming "too dependent on authoritarian powers".
"We are very clear that China poses a challenge to our values and to our interest and to our security and there are many reasons for that," he said, pointing to the crackdown on Hong Kong and Beijing's treatment of minorities in the mainland.
"China doesn't share our values. China and the rulers in Beijing they don't believe in democracy, freedom of speech and our democratic values," he said.
"China is also a challenge because we see that China is investing heavily in mobile military capabilities including long-range missiles that can reach all NATO territory and also this region," he added.
Stoltenberg said it was unclear when the conflict in Ukraine would end, saying Putin was preparing for "more war" and actively acquiring weapons from countries including North Korea.
Pyongyang has denied sending weapons to Moscow, and said Sunday that the United States would face a "really undesirable result" if it persisted in spreading the "self-made rumour".
"Trying to tarnish the image of (North Korea) by fabricating a non-existent thing is a grave provocation that can never be allowed and that cannot but trigger its reaction," said Kwon Jong Gun, director general of the North's Department of US Affairs.
He also called it "a foolish attempt to justify its offer of weapons to Ukraine".
Earlier this week, US President Joe Biden promised 31 Abrams tanks, one of the most powerful and sophisticated weapons in the US army, to help Kyiv fight off Moscow's invasion.