North Korea has vowed to strengthen its nuclear submarine capabilities as South Korea advances plans to build a nuclear-powered submarine, a move analysts say could fuel a naval arms race between the two Koreas and complicate Seoul's push to revive peace talks. According to the North's state-run Korean Central News Agency (KCNA) on Thursday, North Korean leader Kim Jong-un said Seoul's submarine plan would pose a direct threat to Pyongyang. "Saying that the nuclear submarine development plan of the ROK, which Washington has agreed on at the solicitation of Seoul recently, will worsen the instability in the region of the Korean Peninsula, he stressed that the DPRK regards it as an offensive act severely violating its security and maritime sovereignty and a threat to its security that must be countered," KCNA reported, using acronyms for the Republic of Korea and Democratic People's Republic of Korea, the official names of South Korea and North Korea. The North Korean leader made the remarks during a recent on-site inspection of an 8,700-ton nuclear-powered strategic guided missile submar