SEOUL, Dec. 19 (Yonhap) -- The North Korean military and people have pledged to follow the leadership of the late leader's heir apparent Kim Jong-un to carry on the legacy of the communist state, its state media said Monday, amid growing uncertainty over the power transition.

The North's state media reported earlier in the day that 69-year-old Kim Jong-il died of a heart attack two days earlier.

Following that announcement, regional powers are paying close attention to whether Kim's youngest son and heir apparent Jong-un, aged in his late 20s, would successfully take the helm of the impoverished communist state.

"Ten million (North Korean) soldiers and the people are in indescribable grief, after receiving the sad news that comrade Kim Jong-il has died," the North's Korean Central News Agency (KCNA) said. "At this point, faithful belief, optimism and a determined pledge for victory are taking firm root in people's hearts."

The report came hours after Pyongyang urged North Korean soldiers and citizens to remain loyal to the guidance of the new leader and turn "sorrow into strength and courage to overcome the present difficulties and work harder for a fresh great victory."