President Yoon Suk Yeol of South Korea stated on Wednesday that if Russia assisted North Korea in expanding its arsenal in exchange for support in its conflict in Ukraine, that would be “a direct provocation” and Seoul and its allies would not remain silent.

Yoon claimed that such an event would endanger not just the peace and security of Ukraine but also South Korea in an address to the yearly high-level U.N. General Assembly.

Yoon made the comments just as North Korean leader Kim Jong Un returned to Pyongyang from a week-long trip to Russia in which he and Russian President Vladimir Putin vowed to boost military cooperation.

North Korea’s nuclear and missile programs were not only an existential threat to South Korea, but a serious challenge to peace in the Indo-Pacific region and across the globe, Yoon said.

“It is paradoxical that a permanent member of the U.N. Security Council, entrusted as the ultimate guardian of world peace, would wage war by invading another sovereign nation and receive arms and ammunition from a regime that blatantly violates U.N. Security Council resolutions,” he said.

Seoul and Washington have expressed concern that Russia could be trying to acquire ammunition from North Korea to supplement stockpiles thinning as a result of its war in Ukraine, while Pyongyang seeks technological help for its nuclear and missile programs.

“If (North Korea) acquires the information and technology necessary to enhance its WMD capabilities in exchange for supporting Russia with conventional weapons, the deal will be a direct provocation, threatening the peace and security of not only Ukraine, but also the Republic of Korea,” Yoon said.

“The Republic of Korea, together with its allies and partners will not stand idly by.”

Any activities assisting North Korea’s weapons programmes are banned under U.N. Security Council resolutions, and Putin has said Russia, one of the five permanent members of the Security Council, would “never violate anything.”

A South Korean presidential aide rejected this, saying South Korea had been “watching military transactions take place for several months prior to the summit” between Kim and Putin.

On Wednesday, Kremlin spokesman Dmitry Peskov said Russia wants to expand ties with North Korea in all possible areas.

On Tuesday, South Korea’s vice foreign minister, Chang Ho-jin, summoned Russia’s ambassador to urge Moscow to abandon any potential arms deals with North Korea, warning of “clear consequences.”

The South Korean presidential aide said discussions were underway with the United States and other countries to impose more sanctions on Russia and North Korea.

“The Security Council is divided … and it is impossible to draw a unified position on Russia there, so for now there could be cohesive action within the solidarity of freedom, cantering around allies and friends,” the official said.