South Korean President Yoon Suk Yeol left for the 78th United Nations General Assembly on Monday to seek international support against North Korea's recent summit with Russia and promote Busan's 2030 World Expo bid.

In his second attendance to the UN General Assembly since taking office last year, Yoon was expected to deliver a strong message condemning the military cooperation between North Korea and Russia during his keynote speech on Wednesday, Eastern Standard Time.

Earlier last week, North Korean leader Kim Jong-un met with Russian President Vladimir Putin at a Russian space rocket launch site, in spite of international criticism for defying sanctions. The meeting raised suspicions of a deal wherein Russia would replenish its arsenal with North Korean ammunition in exchange for giving cutting-edge military technology information.

Yoon said in a written interview with the Associated Press that the military cooperation between North Korea and Russia is "illegal and unjust," as it infringes UN Security Council resolutions and various other international sanctions. He added that the international community will "unite more tightly" in response to such a move.

The National Security Council stated last week that any action by North Korea and Russia that "threatens our security" in violation of UN Security Council resolutions will "incur a clear price." It also warned of potential military activities between North Korea and Russia, including arms trade.

During his six-day trip to New York, Yoon is also gearing up for a last-minute effort to secure Busan's 2030 World Expo bid ahead of the Bureau International des Expositions' vote to determine the host city in November. First lady Kim Keon Hee also boarded Air Force One on Monday morning, sporting a key ring that read "Busan is ready."

Upon his arrival in New York, Yoon was expected to hold a series of bilateral meetings with participating leaders. He plans to meet with leaders from more than 30 countries bilaterally during his six-day trip to garner support for the Busan Expo, according to presidential office staff before his departure.

According to the presidential office, there are about 10 countries -- including Mauritania, Saint Lucia, North Macedonia and San Marino -- that are pursuing bilateral summits with Korea for the first time since establishing diplomatic ties.

During his visit to Indonesia and India earlier this month, Yoon held bilateral talks with 20 countries to seek support for Busan's World Expo bid. This month alone, he will be holding bilateral talks with at least 50 countries.

Kim Tae-hyo, the deputy national security director, told reporters last week that Yoon would make an all-out effort to secure the country's World Expo bid by meeting with the BIE's voting member countries.

On Thursday, Yoon is set to attend the Digital Vision Forum hosted by New York University, where he is expected to unveil the Digital Bill of Rights. It outlines the foundational direction for a new digital normative order. He also plans to emphasize the importance of solidarity and cooperation within the international community to foster a society where digital prosperity is shared by all.

President Yoon will return to Korea on Saturday.