North Korean's heir apparent appeared to be absent from the entourage on leader Kim Jong-Il's trip to Russia, according to a list announced by the North's state media during the rare visit.
Korean Central News Agency confirmed Sunday Kim's "unofficial visit to Siberia and the Far East" region at the invitation of Russian leader Dmitri Medvedev, calling it a "historic occasion".
A large group of government and military officials were accompanying Kim including defence minister Kim Yong-Chun, vice premier Kang Sok-Ju and Jang Song-Thaek, the leader's brother-in-law and vice head of the powerful National Defence Commission, KCNA said.
But Jong-Un, the leader's youngest son and heir apparent, was not listed in the official entourage.
The young protege, believed to be in his late 20s, was made a general and given senior posts in the ruling communist party last September.
The leader, who suffered a stroke in August 2008, has been grooming his Swiss-educated son as eventual successor in an attempt to extend the family dynasty into a third generation.
Kim Jong-Il took over in the late 1990s from his father and founding president Kim Il-Sung, who built the dynasty that has ruled the impoverished country with an iron first for more than six decades.
Jong-Un, known to be expanding his role in policy-making, has not yet been spotted accompanying his father to diplomatic trips overseas including the leader's surprise visit to China in May.
The visit to Russia comes at a sensitive time for the two countries. Russia is heading into crucial presidential polls in 2012, in which the big unknown is whether Medvedev or former president and current Prime Minister Vladimir Putin will run.
Kim, on his first visit to Russia since 2002, is expected to have talks mid-week with Medvedev, a Russian official said.
North Korea has recently stepped up calls for more food aid from overseas which has dwindled due to global irritation over its nuclear weapons programmes and heightened tensions with South Korea.
The impoverished communist country has relied heavily on international aid to feed its 24 million people since natural disasters and mismanagement devastated its economy in the mid 1990s.