South Korea and China play down claims Kim Jong-un 'fighting for his life' after heart surgery

South Korea and China have cast doubt on claims North Korean leader Kim Jong-un is seriously ill after undergoing heart surgery.

Daily NK, a Seoul-based speciality website, reported late on Monday citing an unnamed source in North Korea that Kim, 36, was recovering after undergoing the procedure on 12 April.

CNN also cited a US official as saying Washington was "monitoring intelligence" that Kim was in grave danger after a surgery.

However, South Korea and China have said they do not believe Kim is fighting for his life.

Two South Korean government sources rejected the CNN report without elaborating on the surgery, according to Reuters. The presidential Blue House said there were no unusual signs coming from the reclusive state building nuclear weapons.

North Korean leader Kim Jong-un attends a meeting in Pyongyang on 11 April. (AP)

An official at the Chinese Communist Party's International Liaison Department, which deals with North Korea, also said the source did not believe Kim was critically ill.

Speculation about Kim’s health was raised after he missed a celebration honouring his late grandfather and state founder Kim Il-sung on 15 April.

He had been seen four days before that at a government meeting.

South Korea’s presidential office said in a statement no suspicious activity had been detected in North Korea that may have given backing to the reports.

North Korean leader Kim Jong-un inspects an air defence unit earlier this month. (AP)

The absence of Kim Jong-il, Kim’s father and predecessor as the country’s leader, from a parade celebrating North Korea’s 60th anniversary in 2008 was followed by rumours that he was in poor health.

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It was later revealed he had a stroke, after which his health declined further until his death in 2011.

Credible information about North Korea and especially its leadership is difficult to obtain and even intelligence agencies have been wrong about its inner workings in the past.

People in a train station in Seoul watch a TV news broadcast on Tuesday showing file footage of North Korean leader Kim Jong-un. (AFP via Getty Images)
There have been reports North Korea's leader Kim Jong-un is recovering from heart surgery. (AFP via Getty Images)

CNN quoted Bruce Klingner, a senior research fellow at the Heritage Foundation and former CIA deputy division chief for North Korea, as saying rumours had circulated recently about Kim’s health.

“There have been a number of recent rumours about Kim’s health (smoking, heart, and brain),” it quoted Klingner as saying.

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“If Kim is hospitalised, it would explain why he wasn’t present on the important April 15th celebrations.

“But, over the years, there have been a number of false health rumours about Kim Jong-un, or his father. We’ll have to wait and see.”

North Korea insists it has not had a single case of coronavirus, but those claims have been challenged by scientists.