An adviser to the South Korean president on Sunday told Fox News the country believed Kim Jong Un, the North Korean leader, was "alive and well."

Speculation about Kim's health has mounted since he has not been seen publicly since April 11 and even missed a celebration to honor his late grandfather — the North Korean founder, Kim Il Sung — on April 15.

According to a report from The Washington Post, both US and South Korean intelligence officials are skeptical of rumors Kim is dead or in grave health.

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An aide to the South Korean president on Sunday said it was his government's official position that North Korean leader Kim Jong Un was "alive and well" amid rampant speculation that Kim was dead or in a vegetative state.

"Our government position is firm," Chung-in Moon, a foreign-policy adviser to South Korean President Moon Jae-in, told Fox News. "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."

As Business Insider reported earlier Sunday, US and South Korean intelligence agencies do not believe that North Korea's authoritarian leader is dead, despite the rumors that have been circulating for more than a week.

According to a Sunday Washington Post report, rumors of Kim's death first began to circulate on April 15, when he was absent from celebrations for the birthday of North Korea's founder, Kim Il Sung, his late grandfather. A South Korean media report said Kim had undergone a heart procedure on April 12 in a hospital outside Pyongyang — the North Korean capital — and was recovering.

Three government officials with knowledge of the situation told The Washington Post that both the US and South Korean governments were skeptical about reports that Kim was dead or in grave condition. Commercial satellite images published by 38 North reportedly showed what was most likely Kim's train on April 21 and April 23 in the coastal resort city of Wonsan in North Korea, according to the report.

Kim has not been publicly seen since April 11.