North Korean leader Kim Jong Il is grooming his middle son as successor, not the youngest son as has been widely speculated, a news report said Wednesday quoting a former political aide who defected.

Kim Jong Chol is holding a secret high-level post in the North's ruling Workers' Party as part of his successor training and reports directly to the leader, Seoul's Dong-a Ilbo newspaper quoted defector Kim Duk Hong as saying.

The 29-year-old "is highly likely to take over the father's post," Kim said.

Who will eventually rule the nuclear-armed North has been the focus of intense media speculation since leader Kim, 67, reportedly suffered a stroke last summer.

Kim succeeded his father, who died in 1994, in communism's first hereditary power succession. He rules the country with absolute authority and has allowed no opposition, raising concerns about a power struggle if he dies suddenly without naming a successor.

Wednesday's report contrasts with widespread media speculation that leader Kim considers the middle son too "girlish" to become leader, and is grooming the third and youngest son, Jong Un, 26, as his successor.

Media reports have said the Swiss-educated middle son is suffering from an excess of female hormones.

Kim's eldest son, Jong Nam, 38, had long been considered the favorite to succeed his father — until he was caught trying to enter Japan on a fake passport in 2001, reportedly telling Japanese officials he wanted to visit Tokyo Disneyland.

The paper said the defector declined to reveal where he obtained the information. He was an aide to former North Korean parliamentary speaker Hwang Jang Yop, and the two defected to the South in 1997. Hwang is the highest-level Pyongyang official ever to defect to Seoul.

Seoul's Unification Ministry and the spy agency National Intelligence Service said they cannot confirm the report.