North Korean leader Kim Jong-il has life-threatening pancreatic cancer, South Korean TV news channel YTN says.
YTN cited unidentified intelligence officials in Seoul and China as sources, but South Korea's spy agency said it could not confirm the story.
YTN said Mr Kim was diagnosed with the illness last year, about the same time he was reported to have had a stroke.
Mr Kim, 67, was seen last week looking gaunt and walking with a limp, fuelling more speculation about his health.
The rare public appearance was at a memorial on 8 July to mark the 15th anniversary of his father's death.
It has been widely reported that Mr Kim's third son, Kim Jong-un, is being groomed as heir, although Pyongyang has made no announcement.
The latest reports on the state of his health come as nuclear negotiators from China and South Korea opened talks in Seoul about how to handle the threat from the North.