North Korean leader Kim Jong Un called for more advanced nuclear weapons and said the United States is “our biggest enemy,”

North Korean leader Kim Jong Un called for more advanced nuclear weapons and said the United States is “our biggest enemy,” state media said on Saturday, presenting a stark challenge to President-elect Joe Biden just days before he takes office.

Washington’s hostile policies would not change regardless of who occupies the White House but dropping those policies would be key to North Korea-U.S. relations, Kim said, according to state news agency KCNA.

“Our foreign political activities should be focused and redirected on subduing the U.S., our biggest enemy and main obstacle to our innovated development,” Kim said during nine hours of remarks over several days at a rare party congress in Pyongyang.

“No matter who is in power in the U.S., the true nature of the U.S. and its fundamental policies towards North Korea never change,” Kim said, vowing to expand ties with “anti-imperialist, independent forces.”

North Korea would not “misuse” its nuclear weapons, Kim said but the country is expanding its nuclear arsenal, including “preemptive” and “retaliatory” strike capabilities and warheads of varying sizes.

Kim called for developing equipment including hypersonic weapons, solid-fuel intercontinental ballistic missiles (ICBMs), spy satellites, and drones.

North Korea is preparing for the test and production of various new weapons, including a “multi-warhead rocket” and “supersonic gliding flight warheads for new type ballistic rockets,” while research on a nuclear submarine is nearly complete, he said.

“Kim pretty much showed what’s on his mind – submarine missiles, better ICBMs and other advanced arms,” said Yoo Ho-yeol, professor of North Korean studies at Korea University in Seoul. “He is saying that’s basically what Washington will see going forward, which could escalate tension or open doors for talks.”

Kim’s remarks were one of the most ambitious outlines of North Korean national defence and nuclear matters in some time, said Ankit Panda, a senior fellow at the U.S.-based Carnegie Endowment for International Peace.

“It could presage a return to nuclear testing, which is now on the table given that Kim renounced his April 2018 moratorium,” he said.