Military cooperation between North Korea and Russia is looming large. The recent summit between North Korean leader Kim Jong-un and Russian President Vladimir Putin is a sight showing that vague concern becomes real risk.

It was a closed-door meeting and no press conference was held. Nothing is known about what they actually discussed, except for their open mention of cooperation in the field of satellites.

Putin said Friday that Russia would not breach any agreements concerning the Korean Peninsula after meeting Kim.

But the prevalent view is that the two leaders may have brokered dangerous deals, calling for North Korea to supply conventional weapons such as artillery shells to be used in Russia's war in Ukraine and for Russia to transfer its latest weapons technologies in return.

Arms trade with North Korea goes against resolutions of the United Nations Security Council.

The Kremlin stressed the need for more cooperation on "sensitive areas that should not be disclosed." This implies that the two leaders were discussing what goes against UNSC resolutions and that they do not care the resolutions.

The UN bans North Korea from making any arms trade. Russia agreed on the adoption of the UN sanctions as one of the few permanent members of the Security Council. Now the country is trying to flout the principles and norms of the international community.

It is a natural consequence for the United States and the international community to express concerns and take warning steps.

The US said Thursday that it was sanctioning more than 150 businesses and people, from Russia to Turkey, the United Arab Emirates and Georgia, to deny the Kremlin access to technology, money and financial channels that fuel Putin's war in Ukraine.

The sanctions package is seen as a warning that Washington will not allow people and companies even in an ally to sell Russia technology that could be used to bolster its war effort.

If follow-up measures on military cooperation are becoming visible after the Russo-North Korean summit, they will likely shake the international security landscape.

If Russia transfers technologies on satellite launching and the atmospheric reentry of an intercontinental ballistic missile to North Korea, the weapons would be a serious threat not only to the Korean Peninsula, but also to the international community. The "sensitive area of cooperation" may include technology related to nuclear-powered submarines.

Transfer of military technology is not only a violation of UN resolutions. It would mean Russia is crossing the line of Seoul-Moscow relations. South Korea's self-defense measures would be inevitable.

The government in Seoul needs to consider proposing to the US a revision of their bilateral atomic energy agreement in a bid to open the way for South Korea to potentially become a nuclear power.

South Korea and its allies must tell Moscow not to cross the red line in connection with North Korea. At the same time they should make more active diplomatic outreach to Russia. Diplomatic efforts must focus on preventing Russo-North Korea relations from developing to the extent of shaking South Korea's security greatly. Its diplomatic responses must be tough depending on the circumstances. Russia must be held responsible if it helps Pyongyang remarkably upgrade its military capability.

South Korea must try to prevent the Putin-Kim summit from escalating confrontation between North Korea, China and Russia on one side and South Korea, Japan and the United States on the other.

A strategic and agile response is required.

President Yoon Suk Yeol is visiting New York from Monday to attend the 78th UN General Assembly. His attendance is significant in that he is debuting on the stage of multilateral diplomacy on the tail of the Kim-Putin summit.

During the UN General Assembly, Yoon should issue a warning message about potential military exchanges between Pyongyang and Moscow. He must seek strong cooperation from the international community to make the two countries rightly pay for their dangerous deal.

With Pyongyang and Moscow getting closer, South Korea should redraw security strategies toward further strengthening deterrence against North Korea.