North Korean leader Kim Jong-un has called the United States the "biggest enemy" of his country, threatening to continue to advance its nuclear capabilities, state media said Saturday, Yonhap reported.

Kim added that Washington's policy against Pyongyang won't change regardless of who rules the White House, saying that an end to its hostile stance will be the key to future relations between the two countries, according to the Korean Central News Agency (KCNA).

Kim made the remarks reporting to the eighth congress of the ruling Workers' Party currently under way in Pyongyang, the first reference to transition of power in Washington since Joe Biden's election as US president in November. They also came days before Biden's inauguration slated for Jan. 20.

The North Korean leader said the US hostile policy has "worsened" despite the North's "efforts" and "maximum patience" to reduce tensions in the region.

Kim rolled out a series of goals to boost its military power. The North also said it has completed the research design of a new nuclear submarine and that it is in the final screening process.

"The reality shows that we need to strengthen the national defense capabilities without a moment of hesitation to deter the United States' nuclear threats and to bring peace and prosperity on the Korean Peninsula," KCNA said.

"(Kim) called for an unrelenting pursuit of building nuclear power for the safety of our people, the fate of our revolution and the existence and self-reliant development of the country," it said.

On South Korea, Kim Jong-un appeared to have left room for improvement in relations, saying the relations could return to three years ago when a peace mood was created "at any time," but emphasized that all depends on South Korea's attitude.