North Korean leader Kim Jong-il's son and heir Jong-un was appointed director of the State Security Department, the regime's chief spy agency, in late 2009.
"Signals intelligence we've obtained suggests Kim Jong-un is being called 'director' of the security department," a South Korean government official said. "It seems he has already gained control of the security agency."
The department's main duties are to ferret out dissidents and put residents under surveillance. It has about 50,000 agents.
At an extraordinary party congress last September, the regime appointed U Dong-chuk, the first deputy director of the department, and Kim Chang-sop, the chief of the political bureau of the department, to the Politburo, the first time in the regime's history that the political bureau chief has joined the top body.
Kim Jong-un visited the department twice in October last year. Kim Jong-il has reportedly headed the department himself since its former chief Ri Jin-su died in 1987.
Kim senior was designated the successor to power in 1974 after he seized control of the party apparatus in 1972 as secretary in charge of organization and propaganda. But Kim Jong-un gained control of the security department first.
Another intelligence report says Kim junior was groomed as the successor in the administration bureau of the powerful National Defense Commission. The regime promoted Gen. Ri Myong-su, the chief of the administration bureau, to minister of public security on April 7.
"The North Korean military is under surveillance by Kim Jong-gak, the first deputy chief of the General Political Bureau," a North Korean source said. "The military and police are effectively under Kim Jong-un's control with Kim Jong-gak and Ri Myong-su acting as the front."