North Korean leader Kim Jong Un has been in a coma for months a South Korean official has claimed.  

A former aid to the South Korean president Kim Dae-jung, Chang Song-min, alleged that Kim has become seriously ill and is in a coma following a botched heart operation. 

He said: “I assess him to be in a coma, but his life has not ended,” he told South Korean media, adding that the leader’s younger sister, Kim Yo Jong, was poised to help lead the country.

“A complete succession structure has not been formed, so Kim Yo-jong is being brought to the fore as the vacuum cannot be maintained for a prolonged period.” 

READ MORE: Kim Jong Un rumours spark succession speculation

It adds fuel to growing speculation that Kim's sister,  Kim Yo-jong, is set to succeed Kim. Questions about Mr Kim’s health flared after he skipped an April 15 commemoration of the 108th birthday of his grandfather, North Korea founder Kim Il Sung.

The National Intelligence Service in South Korea said the power shift partly seeks to “relieve (Kim’s) stress from his reign and avert culpability in the event of policy failure,” the Yonhap News Agency reported.

Mr Kim is the third generation of his family to rule North Korea, and a strong personality cult has been built around him, his father and grandfather.

Kim Yo Jong is in charge of North Korea’s propaganda affairs. 

READ MORE: Issue of the day: Is Kim Jong-un using a body double?

She has frequently appeared with her brother at public activities, standing out among elderly male officials.

She accompanied Kim Jong Un on his high-stakes summits with President Donald Trump and other world leaders. Her proximity to him during those summits led many outsiders to believe she is essentially North Korea’s No.2 official.