(CNN) South Korea continued to pour water on mounting speculation about the health of North Korea's leader Kim Jong Un, telling CNN he is "alive and well."

"Our government position is firm," Moon Chung-in, the top foreign policy adviser to South Korean President Moon Jae-in, told CNN. "Kim Jong Un is alive and well. He has been staying in the Wonsan area since April 13. No suspicious movements have so far been detected."

Questions were raised about Kim's well-being after he missed the celebration of his grandfather's birthday on April 15. He had been seen four days before that at a politburo meeting, according to North Korean state media, KCNA.

CNN reported earlier in the week that the United States is monitoring intelligence that Kim is "in grave danger after a surgery," according to a US official. Another US official told CNN Monday that the concerns about Kim's health are credible, but their severity is hard to assess.

It followed a report by Daily NK, an online newspaper based in South Korea that focuses on North Korea, that Kim reportedly received a cardiovascular procedure because of "excessive smoking, obesity, and overwork." It added that the leader is now receiving treatment in a villa in Hyangsan County.

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