Defense Minister Ahn Gyu-back on Monday warned of a growing security instability surrounding the Korean Peninsula, citing a deepening military cooperation between North Korea and Russia. "The security situation surrounding the Korean Peninsula has become more unstable than ever," Ahn said in a speech at a forum on an alliance with the United States. "North Korea is advancing its nuclear and missile capabilities and modernizing its conventional forces through military cooperation with Russia," Ahn said in the speech. Ahn called such cooperation between North Korea and Russia a "grave challenge," not only to the Korean Peninsula but also to the international community. South Korea's intelligence agency has estimated that North Korea has deployed around 15,000 troops to Russia to support its war with Ukraine since October last year. In return, North Korea was expected to gain access to Russia's cutting-edge military technologies. Last week, North Korea's state media unveiled photos of leader Kim Jong-un inspecting a factory that built an 8,700-ton nuclear-powered submarine. "South Korea and th