North Korean leader Kim Jong Un threatened to expand his nuclear arsenal and develop more sophisticated atomic weapons systems, saying the fate of relations with the United States depends on whether it abandons its hostile policy.

Kim’s comments made Friday during a key ruling party meeting was seen as an effort to apply pressure on the incoming government of President-elect Joe Biden, who is to take office later this month.

The Korean Central News Agency said Saturday that Kim says “key to establishing new relations between (North Korea) and the United States is whether the United States withdraws its hostile policy” on North Korea.

Kim says he won’t use his nukes unless “hostile forces” intend to use their nuclear weapons against North Korea first. But he says North Korea must further strengthen its military and nuclear capability as the danger of a U.S. invasion on North Korea increases.

Kim ordered officials to develop missiles with multiple warhead, underwater-launched nuclear missiles, spy satellites and nuclear-powered submarines.

KCNA says Kim’s order was made during a fourth-day meeting Friday of his country’s first ruling party congress in five years.