North Korea has replaced its long-serving head of state with a close aide to leader Kim Jong Un, promoting a man who was placed on a US sanctions list last year for alleged human rights abuses, state media said Friday.

Kim acquired a new title, and now becomes "the supreme representative of all the Korean people" -- a newly-created role that observers say makes him more like a modern national leader, on a par with other country's presidents and prime ministers.

Kim Yong Nam, the now-91-year-old who held the position of the North's head of state -- an almost entirely ceremonial role -- for almost 20 years, was replaced by Choe Ryong Hae, the state-run KCNA said.