NATO Secretary-General Jens Stoltenberg urged South Korea on Monday to increase military support to Ukraine, citing other countries that have changed their policy of not providing weapons to countries in conflict after Russia's invasion.

Stoltenberg is in Seoul, the first stop on a trip that will include Japan and is aimed at strengthening ties with US allies in the face of the war in Ukraine and rising competition with China.

In meetings with senior South Korean officials, Stoltenberg argued that events in Europe and North America are interconnected with other regions, and that the alliance wants to help manage global threats by increasing partnerships in Asia.

Speaking at the Chey Institute for Advanced Studies in Seoul, he thanked South Korea for its non-lethal aid to Ukraine, but urged it to do more, adding there is an "urgent need" for ammunition. Russia calls the invasion a "special operation".

South Korea has signed major deals providing hundreds of tanks, aircraft and other weapons to NATO member Poland since the war began, but South Korean President Yoon Suk-yeol has said that his country's law against providing arms to countries in conflicts makes providing weapons to Ukraine difficult.

Stoltenberg noted that countries such as Germany, Sweden, and Norway had similar policies but have changed them.

"If we don't want autocracy and tyranny to win, then (the Ukrainians) need weapons, that's the reality," he said.

In a statement carried by state media on Monday, North Korea called Stoltenberg's visit a "prelude to confrontation and war as it brings the dark clouds of a 'new Cold War' to the Asia-Pacific region."

Last year South Korea opened its first diplomatic mission to NATO, vowing to deepen cooperation on non-proliferation, cyber defence, counter-terrorism, disaster response and other security areas.