The meeting, scrutinized for any hint of Mr. Kim's intentions toward South Korea, came as the official North Korean news media announced he had been appointed to the top post of the ruling party, another step in what appeared to be a choreographed sequence of events meant to show that he was assuming all the key positions held by his father, Kim Jong-il, the longtime ruler of the isolated, nuclear-armed North.

South Korea had said it would send no official mourners to Kim Jong-il's funeral, which angered North Korea as a sign of disrespect. But Kim Jong-un's meeting with the private delegation of mourners, which included the former first lady of South Korea and a top businesswoman, appeared to be cordial.

The South Korean visitors, Lee Hee-ho, the widow of former President Kim Dae-jung, and the chairwoman of Hyundai Asan, Hyun Jeong-eun, which had business ties with North Korea, were the only South Koreans allowed by the government in Seoul to lead private delegations to Pyongyang, the North Korean capital, to express sympathy over the death of Kim Jong-il on Dec. 17.

They conveyed their condolences at the Kumsusan mausoleum in Pyongyang, where Kim Jong-il lay in state, according to the South Korean government.

Mr. Kim thanked the South Korean visitors, the official North Korean news agency, K.C.N.A, said.

Ms. Lee and Ms. Hyun laid wreaths and walked around Kim Jong-il's glass coffin to show their respect, K.C.N.A said. In a message in the visitors' log, Ms. Lee wrote that she hoped the two Koreas would achieve an "early reunification" by honoring a 2000 summit agreement in which her husband and Kim Jong-il had promised to encourage political reconciliation and economic exchanges.

Kim Jong-il's funeral is set to take place on Wednesday, and a memorial is scheduled for Thursday.

Kim Jong-un's announced elevation to the leadership of the Workers' Party's Central Committee came two days after the North's state-run news media published an entreaty for him to become supreme commander of the Korean People's Army, whose support is considered crucial to his consolidation of power. The top officers also moved quickly to swear their allegiance to Mr. Kim.

Since Kim Jong-il's death was announced on Dec. 19, a series of pronouncements from North Korea have indicated that Kim Jong-un, his third and youngest son, was rapidly consolidating his grip on power by assuming top titles, or that whoever was rallying the key agencies of power behind the young leader was ensuring that the son would not share power, at least in the public eye.

Kim Jong-un is believed to be in his late 20s. There has been no indication that he had worked in the government or the military before his father, who had a stroke in 2008, unveiled him as his successor last year and put him on a path to be groomed as heir.

On Monday, the North's main newspaper, Rodong Sinmun, urged North Koreans to "defend the party's Central Committee headed by respected Comrade Kim Jong-un."

The same slogan was used for his father when he was alive. Over the weekend, the North Korean news media were giving the son the same honorifics previously reserved for his father: "heaven-sent leader," "the sun of the 21st century" and eobeoi, the Korean word for parent, which North Korea has used only for Kim Jong-il and his father, Kim Il-sung, the North's founding president.

Under the charter of the Workers' Party, the head of its Central Committee doubles not only as general secretary but also as chairman of the party's Central Military Commission.

Kim Jong-un was made vice chairman of the Central Military Commission when he was chosen as successor.

The Seoul government said that Ms. Lee and Ms. Hyun were reciprocating for the North Korean delegations that visited Seoul to express condolences over the deaths of Kim Dae-jung and of Chung Mong-hun, the former Hyundai chairman.

Hyundai Asan led a flurry of South Korean investments that followed a 2000 meeting between leaders of the two Koreas. But the South suspended its signature project in North Korea, a hiking and spa resort near the North's Diamond Mountain, after North Korean guards shot and killed a South Korean woman, a tourist who had strayed off the resort in 2008.