North Korean officials say they will not invite foreign delegations and will allow no entertainment during the mourning period.
Kim's death and the possibility of a power struggle in a country armed with nuclear weapons and known for its unpredictability has heightened tensions in the region.
North Korean state media have given clear indications that Kim's third son will succeed him.
The Korean Central News Agency on Tuesday described Kim Jong Un as a "a great person born of heaven," a propaganda term only his father Kim Jong Il and his grandfather Kim Il Sung had enjoyed. The Rodong Sinmun, the newspaper of the ruling Workers' Party, added in an editorial that Kim Jong Un is "the spiritual pillar and the lighthouse of hope" for the military and the people.
It described the twentysomething Kim as "born of Mount Paektu," one of Korea's most cherished sites andKim Jong Il's official birthplace. On Monday, the North said in a dispatch that the people and the military "have pledged to uphold the leadership of comrade Kim Jong Un" and called him a "great successor" of the country's revolutionary philosophy of juche, or self reliance.