Kim Jong Un has rapidly gained prominence since the death of his father Kim Jong Il on December 17, and his brief meeting with a group led by a former South Korean first lady and a prominent business leader shows Seoul that he is assured in his new role.
State media have showered Kim with new titles.
On Saturday, the North referred to him as "supreme leader" of the 1.2 million-strong armed forces and said the military's top leaders had pledged their loyalty to him. On Monday, the Rodong Sinmun newspaper described him as head of the Central Committee of the Workers' Party - a post that appears to make him the top official in the ruling party.
Also on Monday, a South Korean delegation stood in a line on a red carpet and bowed silently during their visit to the Kumsusan Memorial Palace, where Kim Jong Il's body is lying in state in a bier surrounded by flowers and flanked by an honor guard.
Kim Jong Un gave the South Koreans his thanks after they expressed condolences and sympathy, the North's official Korean Central News Agency said. Seoul's Unification Ministry confirmed the meeting in a statement but didn't elaborate.
The lead delegates were the widow of former South Korean President Kim Dae-jung, who engineered a "sunshine" engagement policy with the North and held a landmark summit with Kim Jong Il in 2000, and Hyundai Group Chairwoman Hyun Jeong-eun, whose late husband had ties to the North.
Their meeting with Kim Jong Un could be intended to push South Korea to pursue previously agreed upon co-operative projects that would give North Korea much-needed aid, said Yang Moo-jin, a professor at the University of North Korean Studies, which is in South Korea.
Footage from AP Television News in North Korea earlier showed the South Koreans being greeted by North Korean officials during a stop at a factory park in the North Korean border town of Kaesong. North Korea sent delegations to Seoul when the women's husbands died.
The meeting appeared to be Kim Jong Un's first reported meeting with South Koreans since his father's death.
The Kim family has extended its control over the country of 24 million people to a third generation with Kim Jong Un, who is in his late 20s and was revealed last year as his father's choice among three sons for successor.
Kim Jong Il, who ruled North Korea for 17 years, wielded power as head of three main state organs: the Workers' Party, the Korean People's Army and the National Defense Commission. His father, North Korea founder Kim Il Sung, remains the nation's "eternal president" long after his 1994 death.
Kim Jong Un was named a vice chairman of the Central Military Commission of the Workers' Party last year, but was expected to ascend to new military and political posts while being groomed to become the next leader.
The reference to his new title was in commentary in the Rodong Sinmun newspaper, the mouthpiece of the Workers' Party, urging soldiers to dedicate their lives "to protect the party's Central Committee headed by respected Comrade Kim Jong Un."
Rodong Sinmun has also called on the people to become "eternal revolutionary comrades" with Kim Jong Un, "the sun of the 21st century."
The language echoed slogans used years ago to rally support for Kim Jong Il, and made clear the son is quickly moving toward leadership of the Workers' Party, one of the country's highest positions, in addition to the military.
North Korea refers to Kim Il Sung as the "sun" of the nation and his birthday is celebrated as the "Day of the Sun," and state media have sought to emphasise Kim Jong Un's role in carrying out the Kim family legacy throughout his succession movement.
His titles are slight variations of those held by his father, but appear to carry the same weight. It was unclear whether the nation's constitution had been changed to reflect the transfer of leadership as when Kim Jong Il took power after his father's death.
Mourning continued, meanwhile, despite frigid winter weather, in the final days before Kim Jong Il's funeral is set to take place on Wednesday and a memorial on Thursday.
People continued lining up in central Kim Il Sung Square, where a massive portrait that usually features Kim Il Sung has been replaced by one of Kim Jong Il, to bow before his smiling image and to lay funereal flowers. Heated buses stood by to give mourners a respite from the cold, and hot tea and water were distributed from beverage kiosks.
