The report in the Dong-a Ilbo newspaper cited an unnamed government official in saying intelligence obtained Sunday suggested "a serious problem" with Kim's health. The report did not elaborate, and South Korea's National Intelligence Service and Unification Ministry said Wednesday they could not confirm it.
Kim, 66, reportedly suffered a stroke and underwent brain surgery in August. A Japanese TV station says his eldest son went to Paris to recruit a neurosurgeon who was flown back to Asia to treat Kim.
The Dong-a report came a day after Japan's prime minister told lawmakers in Tokyo that Kim probably is in the hospital, though "not unable" to make decisions as North Korea's leader.
The chief of the National Intelligence Service had told lawmakers Tuesday that Kim was "not physically perfect" but still able to rule the country.
North Korea denies Kim is ill, However, speculation about the reclusive leader's health grew when he missed a September military parade marking North Korea's 60th anniversary. He then disappeared from public sight for two months.
Kim, who rules the Stalinist nation with absolute authority, has not publicly named any successors, leading to concerns about an uncertain future in the impoverished, nuclear-armed nation.
North Korea has sought in recent weeks to tamp down rumors about Kim's health with news reports and footage portraying the leader as active and able, attending a soccer game and inspecting a military unit. The reports, photos and video are undated.
The latest footage, aired Monday and Tuesday on North Korean television, showed Kim hitting the road earlier this year to tour farms and factories and to see the sights across the communist North.
The 50-minute montage set to patriotic music showed a sprightly Kim in his trademark jumpsuit and sunglasses -- and wearing a winter parka, his hair blowing in the wind, in footage shot in May, months before his reported stroke.
Experts say the photos and footage shown in recent weeks appear to have been taken several months ago, before Kim's reported stroke.
Japan's Fuji television reported Monday that Kim's eldest son, Kim Jong Nam, flew recently to Paris to recruit a neurosurgeon to treat his father.
Japanese Prime Minister Taro Aso told lawmakers Tuesday that the French doctor got on a plane for Beijing, perhaps en route to North Korea. South Korea's NIS chief Kim Sung-ho also said the son was believed to have traveled to France recently.
French neurosurgeon Francois-Xavier Roux denied Wednesday that he was on a secret mission to North Korea to treat Kim. Reached by The Associated Press on his cell phone, the physician said he was in Beijing for a meeting of neurosurgeons -- "nothing extraodinary."
"If I was at Kim Jong Il's bedside, I wouldn't be answering the phone," Roux said. "I am in Beijing. I am staying in Beijing."
Roux told the AP that his trip to China has no link with Kim. He blamed the confusion on "a Japanese TV station (that) has done some brainwashing, some manipulation," apparently referring to the Fuji television report.