SEOUL, South Korea — North Korea confirmed on Monday that Jang Song-thaek, the uncle of Kim Jong-un, the country’s top leader, had been stripped of all titles of power and expelled from the ruling Workers’ Party of Korea. Mr. Jang is the most prominent figure to be purged since Mr. Kim took power two years ago.

Moving swiftly to consolidate his authority, Mr. Kim presided over an extended meeting of the Political Bureau of the Party Central Committee on Sunday, which formalized the sidelining of Mr. Jang, 67, who had been considered the second most powerful person in North Korea after Mr. Kim.

A number of Mr. Jang’s associates also were purged, according to a lengthy report by the state-run Korea Central News Agency, which called them “a modern-day faction” and “undesirable elements who happened to worm their ways into our party ranks.” Mr. Jang and his “group” were accused of committing “such anti-party, counterrevolutionary factional acts as expanding their forces through factional moves” and “attempting to undermine the unitary leadership of the party.”

South Korean intelligence officials said the language in the report was a signal that Mr. Kim, who is 30, was uprooting a wide network of protégés Mr. Jang had placed in party and military posts, and doing it in a way that was meant to send a strong signal to others in the country’s elite that he is firmly in charge. The report said that other Central Committee members, representatives from provincial party committees and the People’s Army attended the meeting as observers.