- Its policy towards the North "will never change, whoever comes into power", he added, without mentioning Biden by name.
SEOUL: North Korean leader Kim Jong Un pledged to strengthen his country's nuclear arsenal as he delivered his closing address to a top ruling party meeting, state television showed Wednesday, days before Joe Biden takes office as US president.
Kim is looking to grab the attention of the incoming Biden administration, analysts say, with his country more isolated than ever after closing its borders to protect itself against the coronavirus pandemic.
A nuclear summit between Kim and outgoing US President Donald Trump in Hanoi in February 2019 broke down over sanctions relief and what Pyongyang would be willing to give up in return.
"We must further strengthen the nuclear war deterrent while doing our best to build up the most powerful military strength," Kim told the Workers' Party congress, footage broadcast on Korea Central Television showed.
Thousands of delegates and attendees -- none of them wearing masks -- repeatedly rose to their feet in the cavernous April 25 House of Culture venue to interrupt his speech with applause.
Earlier in the eight-day meeting, which has lasted twice as long as the previous gathering in 2016, Kim called the US "the fundamental obstacle to the development of our revolution and our foremost principal enemy".
Its policy towards the North "will never change, whoever comes into power", he added, without mentioning Biden by name.
The North had completed plans for a nuclear-powered submarine, he said -- a strategic game-changer -- and offered a shopping list including hypersonic gliding warheads, military reconnaissance satellites and solid-fuel intercontinental ballistic missiles (ICBMs).
Pyongyang's weapons programmes have made rapid progress under Kim, and at a parade in October it showed off a huge new ICBM that analysts said was the largest road-mobile, liquid-fuelled missile in the world.
The change of leadership in Washington presents a challenge for North Korea: Biden is associated with the Obama administration's "strategic patience" approach and characterised Kim as a "thug" during the presidential debates.
The North, meanwhile, has called Biden a "rabid dog" that "must be beaten to death with a stick".
Kim and Trump had a tumultuous relationship, engaging in mutual insults and threats of war before an extraordinary diplomatic bromance featuring headline-grabbing summits and declarations of love by the outgoing US president.
Kim's latest comments built on his rhetoric earlier in the congress while leaving a door open for dialogue, said Hong Min of the Korea Institute for National Unification in Seoul.
"It is a message to the US that it will continue to build up its strategic arsenal unless the US changes its course on North Korea policy," he told AFP.
"If Washington treats it nicely, it will act nice, but if it treats it harshly, it will act harshly too."