"These are thoughts which cannot be completely suppressed and if in fact it goes that way, and South Korea and Japan go closer to being nuclear powers or actually cross the threshold, it means a different strategic and security balance in northeast Asia," Lee said on Thursday. Not only would that scenario produce more risk and tension, "the Chinese will be very alarmed," he added. "I don't think that will make for a safer world, there will be implications elsewhere in the world." The current tensions are not just dangerous because of the chance of immediate flare ups, but also because they may introduce "longer-term trends, which are set off in northeast Asia if things persist in this direction," the 65 year-old leader said.

Singapore PM Lee Hsien Loong Terence Tan | MCI | Getty Images

Last month, South Korean Defense Minister Song Young-moo and Secretary of Defense Jim Mattis discussed the prospect of returning American nukes to Asia's fourth-largest economy. Washington stationed nuclear weapons in South Korea in 1958 but withdrew them in 1991. Former Japanese Defense Minister Shigeru Ishiba also suggested placing American nuclear weaponry on Japanese territory last month. Both governments, however, dismissed the idea.

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