The son of North Korean leader Kim Jong-Il has cemented his status as leader-in-waiting through frequent field trips with his ailing father, the South's unification ministry said Monday.

Kim Jong-Un has accompanied his father 100 times, or on two-thirds, of his trademark "field guidance" trips, since he was confirmed as leader-in-waiting a year ago, the ministry said in a report.

Jong-Un, believed to be in his late 20s, was made a general and given senior communist party posts on September 28 last year.

Since then all of the son's public appearances have been alongside his father, the ministry said.

The 69-year-old leader, who took over after his own father and founding president Kim Il-Sung died in 1994, has apparently speeded up plans for a second eventual dynastic succession since suffering a stroke in August 2008.

It remains unclear when the son will be formally named as successor but the ministry said the son was already actively involved in state affairs.