SEOUL (Reuters) - 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. North Korean leader Kim Jong Un speaks during the 8th Congress of the Workers" Party in Pyongyang, North Korea, in this photo supplied by North Korea"s Central News Agency (KCNA) on January 9, 2021. KCNA/via REUTERS “It could presage a return to nuclear testing, which is now on the table given that Kim renounced his April 2018 moratorium,” he said. U.S. TALKS STALLED There was no immediate comment from the U.S. State Department. A spokesman for the Biden campaign declined to comment. Kim criticised South Korea for offering cooperation in “non-fundamental” areas such as coronavirus aid and tourism, and said Seoul should stop buying arms from and conducting military drills with the United States. South Korea’s Unification Ministry said it still hopes for a better North Korea-U.S. relations, and will continue to pursue the denuclearisation of the Korean peninsula. “The inauguration of the new U.S. administration can be a good opportunity to improve U.S.-North Korea relations, and we expect relations to swiftly resume,” the ministry said in a statement after Kim’s comments were released. Biden, who was vice president under President Barack Obama, called Kim a “thug” during the election campaign. In 2019 North Korea called Biden a “rabid dog” that needed to be “beaten to death with a stick.” Kim had three unprecedented meetings with President Donald Trump and the two corresponded in a series of letters, but those efforts failed to lead to a denuclearisation deal or official change in the countries’ relations. “North Korea is declaring the window for cooperation is much, much smaller for the Biden administration,” Yoo said. Biden said in October that he would meet Kim only on the condition that North Korea agreed to draw down its nuclear capacity. Last month Kurt Campbell, the top U.S. diplomat for East Asia under Obama and considered a contender for a top Asia policy position under Biden, said the incoming U.S. administration would have to make an early decision on what approach it will take with North Korea and not repeat the delay of the Obama era. ‘SELF-RELIANCE’ Besides U.S. and defence policy, Kim spoke at greater length on proposals for a five-year economic plan due to be announced at the congress, which he said would continue a focus on building an independent economy. “The basic seeds and themes of the new five-year economic development plan are still self-reliance and self-sufficiency,” he said. Among the plans are building energy-saving steel plants, significantly increasing chemical goods, boosting electricity production, and securing more coal mines, Kim said. The congress took steps toward “strengthening the united guidance and strategic management of the state over the economic work.” North Korea faces growing crises caused by international sanctions over its nuclear programme, as well as self-imposed lockdowns to prevent a coronavirus outbreak. “In practical terms, there’s a disconnect between North Korea’s dire internal economic situation and this ambitious nuclear and military modernisation agenda,” Panda said.