South Korean President Yoon Suk-yeol has denounced military cooperation between Russia and North Korea, calling it "a direct provocation" against his country.

In a keynote address to the UN General Assembly in New York on Wednesday, Yoon also said the North's nuclear and missile programs pose a serious challenge to peace in the Indo-Pacific region and across the world.

Yoon's statement followed a meeting between North Korean leader Kim Jong Un and Russian President Vladimir Putin last week. They reportedly agreed to expand military cooperation.

Yoon said that "the deal will be a direct provocation," threatening the peace and security of not only Ukraine, but also South Korea.

He added that South Korea, "together with its allies and partners, will not stand idly by."

Yoon also called on countries to support South Korea's bid to host the 2030 World Expo in Busan, its second largest city. He noted that Busan links the Eurasian continent with the Pacific Ocean.

He said South Korea hopes to use the event to share its experience of growth and development with the world.