The KM-SAM Cheongung missile system. Photo credit: AFPUkraine has urged South Korea to provide air-defence systems to help protect its forces from Russian missile and drone attacks, with Ukrainian President Volodymyr Zelenskyy making the appeal as North Korea deepens its military involvement in Russia’s war.In a social media post on Saturday, Zelenskyy said a decision had been made to deploy between 30,000 and 50,000 North Koreans to Russia, a figure higher than his previous estimate of 30,000 in July. He did not provide further details or explain the basis for the latest estimate.Against this backdrop, Zelenskyy called for closer cooperation between South Korea and Ukraine, saying Seoul could support Kyiv with what it currently lacks most, air-defence systems. In return, Ukraine could share its battlefield experience and expertise in drone technology with South Korea, he said.Zelensky also acknowledged that South Korea faces legal restrictions on supplying weapons to countries involved in war. While saying the decision ultimately rests with Seoul, he stressed that Ukraine was seeking greater defence cooperation and that diplomatic contacts between the two countries were ongoing.North Korea’s growing military role in RussiaUkraine’s latest warning comes as North Korea continues to expand its military involvement in Russia’s war. Ukrainian military intelligence has reported that a North Korean missile unit has begun deploying personnel and equipment to western Russia, potentially involving around 90 personnel, six launchers and up to 120 ballistic missiles for use against Ukraine.Cho Han-bum, a senior research fellow at the Korea Institute for National Unification, said North Korea may be seeking advanced military technology from Russia in return for its military support. He said Kim could view North Korea’s military assistance as a favour that now needs to be repaid by Moscow.Since Kim and Putin signed a comprehensive strategic partnership treaty in June 2024, Pyongyang is believed to have sent around 20,000 combat troops and military engineers, mainly to Russia’s Kursk region. South Korean intelligence estimates that around 6,000 North Korean troops have been killed or wounded, while the BBC has estimated about 2,300 deaths.Cho said sending another 30,000 to 50,000 troops would be difficult for Pyongyang, particularly if elite forces are involved. The 11th Corps, also known as the Storm Corps, is one of North Korea’s key special-operations formations, and heavy casualties could weaken the country’s military capabilities. A major loss of elite troops could also create political risks for Kim Jong-un.South Korea’s dilemmaSouth Korea faces a difficult choice over Ukraine’s request for air-defence systems. While Seoul has supported Ukraine with assistance in areas such as energy, infrastructure, healthcare and education, its defence exports remain subject to domestic laws and policies.Even if South Korea decides to provide air-defence systems, production capacity could be a constraint. Doo Jin-ho, director of the Eurasia Research Centre at the Korea Research Institute for National Strategy, said Seoul cannot rapidly increase production while also meeting demand from other countries.The dilemma is also geopolitical. South Korea’s relations with Russia have deteriorated since Seoul joined sanctions over the Ukraine war, while Russia has deepened its military cooperation with North Korea. Supplying advanced air-defence systems to Kyiv could further strain those ties.For Seoul, the decision therefore comes down to balancing support for Ukraine, its own defence needs, limited production capacity and the growing Russia-North Korea military partnership.