North Korean leader Kim Jong Un has promoted his 28-year-old sister to the ruling party’s political wing, bringing her closer to the center of power and tightening the family’s control on the regime.

The promotion of Kim Yo Jong took place at a Workers’ Party convention Saturday in Pyongyang, where Kim Jong Un called for continuing nuclear-arms development to defend against what he called “U.S. imperialists’ nuclear blackmail,” according to the official Korean Central News Agency.