(Bloomberg) -- South Korea is considering whether to end its ban on sending lethal weapons to Ukraine after Russia and North Korea reached a new military pact, a move that could see Seoul’s large stores of artillery shells heading to Kyiv.

South Korea will reevaluate its policy on prohibiting the export of lethal aid to countries such as Ukraine, national security adviser Chang Ho-jin said in a news briefing Thursday. He expressed grave concern over the pact between Moscow and Pyongyang that Seoul sees as a violation of United Nations Security Council resolutions.

Russian actions that harm South Korea’s security will inevitably have a negative impact on South Korea-Russia relations, he said. South Korean government policy prohibits lethal aid to countries at war. 

“We plan to reconsider the issue of arms support to Ukraine,” Chang was quoted as saying by Yonhap News.

During a visit to North Korea on Wednesday, President Vladimir Putin and North Korean leader Kim Jong Un reached a deal to provide immediate military assistance if one of them is attacked, reviving an agreement dating back to the Cold War. 

The move raised worries among two close US allies, South Korea and Japan, both of whom host American troops and are in the firing line of North Korea’s ballistic missiles. Japan’s top government spokesman Yoshimasa Hayashi told reporters at a news briefing that Tokyo is “seriously concerned” about the military pact’s impact on regional security.

Last year, the Kremlin said if South Korea supplies arms to Ukraine it would make it a participant in the conflict, with former Russian president Dmitry Medvedev suggesting Moscow could respond by selling advanced weaponry to North Korea.

The Koreas have two of the world’s largest artillery forces, with thousands of large caliber guns pointed at each other across the demilitarized zone that separates them. Their stockpiles of shells include North Korean ones that are inter-operable with Soviet-era artillery that Russia has deployed to the front-lines in its war. South Korean 155 mm caliber shells meanwhile are the standard used by the NATO countries supplying Ukraine, weapons experts have said.

The US, South Korea and Japan have accused Kim’s regime of sending munitions and ballistic missiles to aid Putin in his grinding war on Ukraine. North Korea has sent containers to Russia that could hold nearly 5 million artillery shells, South Korean Defense Minister Shin Wonsik said in an interview with Bloomberg News last week.

In return for the munitions, Russia has aided North Korea in its quest to deploy an array of spy satellites, in addition to selling it conventional arms such as tanks and aircraft, Shin said. Moscow and Pyongyang have denied the arms transfers despite ample evidence showing them taking place.

While Ukrainian officials raised the alarm about the threat of a Russian breakthrough during months of delays over US arms deliveries, Kyiv’s troops have mostly held the line despite being outgunned as much as 10-1 by Moscow’s invading army.

--With assistance from Shinhye Kang.

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