North's leader Kim Jong-un visits the Central Cadres Training School of the Workers' Party of Korea, Monday, in this image released by the Korean Centreal News Agency the following day. Yonhap

North Korean leader Kim Jong-un has visited a key political school of the ruling Workers' Party of Korea (WPK) to mark its 80th founding anniversary, calling it a "strategic fortress" ensuring the party's existence, state media reported Tuesday.

Kim paid a "congratulatory" visit to the Central Cadres Training School of the WPK the previous day, accompanied by senior party officials, according to the Korean Central News Agency (KCNA).

The Central Cadres Training School is North Korea's top political education institution designed to cultivate and reeducate party cadres.

The school is "now glorifying its sacred original name ... as a strategic fortress guaranteeing the existence and development of the Party," Kim was quoted as saying in a speech by the KCNA.