North Korea has hit out at South Korea's president and other "foolish politicians" if they think Pyongyang will change after the death of leader Kim Jong Il.

The message, attributed by North Korea's state media to the powerful National Defense Committee, comes only a day after Kim Jong Il's youngest son Kim Jong Un was described for the first time as "The Great Leader."

"We declare solemnly and confidently that the foolish politicians around the world, including the puppet group in South Korea, should not expect any change from us," the NDC was quoted as saying.

Intense international speculation has surrounded the rapid rise to power of Kim Jong Un, of whom little is known. Even his exact age -- believed to be 27 or 28 -- is unclear.

His father, who had been chairman of the NDC, ruled the North with an iron fist since the death of his own father, Kim Il Sung, in 1994. But Kim Jong Il's death of a heart attack Dec. 17 has made nervous many Asia-Pacific countries, as well as Western powers including the United States.

In the past decade South Korea gone on high alert after several unprovoked, brief but limited military attacks which has cost dozens of lives south of the 1953 cease-fire line.

The nervousness is especially acute because North Korea has conducted nuclear weapons tests. Any normalization of relations with the wider international community is bound up with neutralizing its suspected capability to produce nuclear weapons. The six-nation denuclearization talks between North and South Korea, China, United State, Russia and Japan have been stalled for months.

But the latest message from the NDC reiterated Pyongyang's hard-line stance against the international community in general and in particular South Korea, saying it is business as usual.

This week the North Korean government ended the official period of mourning with a national memorial service for Kim Jong Il. Rhousands of soldiers and people crowded Pyongyang's main square for the ceremonies.

At center stage was Kim Jong Un, who received the backing of the military's main leaders, the "Gang of Seven," a report in the South Korean newspaper Chosun Ilbo said. Along with Kim Jong Un, they walked alongside the hearse carrying the body of Kim Jong Il, a public declaration that they stand behind their young leader, the report said.

Kim Jong Un's family connections to the military and other powerful bodies run deep. His uncle Jang Song Taek, is an influential figure in the Workers Party and spent a long time in the party's Organization and Guidance Department, which plays the role of a commissariat.

Although Kim Jong Un has little military background, his two dead older brothers were generals -- Kim Song U died in 2009 and Kim Song Gil died in 2006.

As the year closes, diplomatic activity in the region is set to intensify as countries come to grips with what the change in leadership means in reality, rather than party political rhetoric. Kurt Campbell, assistant secretary for East Asian and Pacific Affairs in the U.S. State Department, will visit Beijing, Seoul and Tokyo in early January.

Even China, Pyongyang's ardent backer since the 1953 armistice that split the Korean Peninsula, will have questions to ask of the new "Great Leader."

Millions of people starved to death during the first four years of Kim Jong Il's rule starting in 1994, an editorial in Chosun Ilbo said. Hundreds of thousands fled North Korea in search of food and jobs.

The editorial points to the "miserable legacy" of Kim Jong Il as being one of hunger for the population in what is one of world's poorest nations but with a suspected nuclear weapons capability.

China, which began liberalizing its economy in the late 1970s and is a world economic power, may lose patience with its small isolationist ally. "Kim Jong Il marched blithely in the opposite direction," the editorial noted.

"At this moment, China might provide the best chance of stability," Robert Carlin, a former U.S. State Department official and fellow at Stanford University, said in a New York Times report earlier this month.

"They want to be the best informed and have a modicum of influence and have people consulting with them at this moment," Carlin said. "The rest of us are deaf, dumb, blind and with our arms tied behind our backs."

Apart from helping prop up a failing North Korean economy, China has had to back its ally in face of heavy international criticism over unprovoked attacks on the South. The Times' article noted that Chinese officials have pushed North Korea's generals to show more prudence to ensure no repeat of the sudden shelling of South Korea's Yeonpyeong Island last year.

Also last year, China was put in an awkward position when South Korea accused North Korea of sinking the Cheonan, a South Korean warship, with loss of 46 sailors.

An international investigation pointed the finger at Pyongyang for the sinking, which it denied. But the episode underlined China's limited patience.