SEOUL, Dec. 19 (Yonhap) -- The sudden death of North Korean leader Kim Jong-il triggered speculation over whether his heir-apparent son, Kim Jong-un, will take over the country as planned.

Kim Jong-un has been groomed as the leader-in-waiting since last year when he was named vice chairman of the Central Military Commission of the ruling Workers' Party and a four-star general.

Kim is expected to try to strengthen his political base by displaying his allegiance toward his late father in coming years as his late father did for the country's founder Kim Il-sung, who died in 1994.

Kim was named as chair of the North's commission for his late father's funeral, which is set for Dec. 28, according to the North's state media.

Still, it was not immediately clear whether the untested leader-in-waiting, in his late 20s, will be able to lead the country.

South Korea's Unification Minister Yu Woo-ik said last month that there are unfavorable conditions for the power succession.

Kim Jong-un is likely to have to rely on Jang Song-thaek, late Kim's brother-in-law and vice chairman of the North's powerful National Defense Commission, as the North's young leader builds his political base in coming years.

Jang, who is married to the late leader's younger sister, Kim Kyong Hui, has been involved in security and defense affairs as well as projects to attract foreign investment.

Jang has long been considered a key regent in helping to smooth the way for a third-generation power transition to Kim Jong-un.

However, it was not clear whether Jang will help Jong-un become the country's next leader, given his strong influence in the North.

There is also speculation that the North's military, a key backbone of late Kim's rule, could try to keep the heir-apparent son in check and assume power.

Some also speculated that the North's defense minister, Kim Yong-chun, could join hands with Jang to enthrone a new leader, possibly, Kim Jong-nam, the late Kim's oldest son.

Jong-nam is believed to have been staying in China since 2001, when he was caught trying to visit Disneyland in Tokyo with his son and wife on a forged passport.

"Internal power struggles could pose more of a threat to Kim Jong-un than external factors," a North Korea expert said, noting late Kim spent nearly 20 years building support before assuming power, but Kim Jong-un has to stand on his own feet. The expert asked not to be identified, citing policy.