The promotion of North Korean leader Kim Jong Un's 28-year-old sister to the country's top decision-making body is a sign he is strengthening his position by drawing his most important people closer to the center of power, experts and officials say.

Kim Yo Jong was named as an alternate member of the Politburo within the ruling Workers' Party of Korea, the opaque, all-powerful party organ where top state affairs are decided, the North's official media said Sunday.

It makes her only the second woman in patriarchal North Korea to join the exclusive club after Kim Kyong Hui, who held powerful roles when her brother, Kim Jong Il, ruled the country.