SEOUL—North Korea condemned the U.S.’s new national-security strategy and vowed to build a nuclear arsenal to match Washington’s ahead of a United Nations Security Council vote that could expand sanctions on the regime.

The comments, released via Pyongyang’s state media Friday, appeared to rule out eventual denuclearization, a goal long sought by the U.S. and its allies. Analysts in Seoul cautioned against drawing conclusions, saying the North often engages in bluffing.

The...