SEOUL (AFP) - North Korean leader Kim Jong Un has replaced officials holding almost half of the nation's key posts in an attempt to strengthen his control over the country, a South Korean report showed on Tuesday.

Mr Kim has changed the officials filling 97 out of 218 military, party and government posts since he took over the communist dynasty in December 2011, the South's Unification Ministry said in a report.

He has often used a "demotion and reinstatement" process in reshuffling military posts in an attempt to tighten control over the military, the ministry said.

"This means Kim has completed the dynastic succession of power successfully and faster than expected," Professor Yang Moo Jin at Seoul's University of North Korean Studies told AFP.

He said Mr Kim had replaced old appointees dating from his father's era with relatively young figures loyal to himself.

The South's spy agency said in a separate report to parliament that Mr Kim had stepped up a campaign to build up a personality cult around himself.

Despite chronic food shortages, Mr Kim has spent about US$300 million (S$374 million) on building leisure and sports facilities including a ski resort, the National Intelligence Service said.

The Masik ski resort has been under construction as one of Kim's pet projects.

Mr Kim wanted the facility - with 110km of multi-level ski runs, a hotel, heliport and cable cars - completed by the end of the year.

The Kim family dynasty has ruled North Korea with an iron fist and a pervasive personality cult for more than six decades.

Mr Kim Jong Un, grandson of founding leader Kim Il Sung, took over when his own father Kim Jong Il died of a heart attack in December 2011.