Kim Jong Un has signalled plans to develop new nuclear weapons and described the US as North Korea’s “biggest enemy”, moves that threaten to raise tensions with US president-elect Joe Biden.

The North Korean leader’s comments, made at a rare gathering of top political officials in Pyongyang, marked the dictator’s strongest broadside against Washington since Mr Biden won the presidency in November’s election.

“Our external political activities going forward should be focused on suppressing and subduing the US, the basic obstacle, biggest enemy against our revolutionary development,” Mr Kim said, according to a translation by South Korea’s Yonhap news agency.

Analysts warn that North Korea’s nuclear weapons development represents a core foreign policy challenge for Mr Biden, who faces unprecedented domestic problems and a tumultuous transition of power.

“It is quite clear Kim is sending Biden the signal that dealing with North Korea will remain a tough challenge — whether or not the administration chooses to prioritise the North Korean threat is irrelevant to Kim,” said Soo Kim, a former CIA North Korea analyst now at Rand Corporation, a US think-tank.

The Kim regime has announced a series of weapons development plans, including shorter-range “tactical” nuclear weapons, a new nuclear submarine, and hypersonic missiles, according to a separate report released by North Korean state media.

Ankit Panda, a North Korea weapons expert at the Carnegie Endowment for International Peace, said the report “lifts the curtain” on recent modernisation carried out “quietly” by the regime’s scientists and munitions industry, and also signalled a return to dangerous nuclear weapons tests.

“I find the explicit mention of tactical nuclear weapons concerning . . . [that] would be an important postural shift that could result in dangerous changes in organisational command and control practices in North Korea,” Mr Panda said.

The latest statements from Pyongyang follow several years of unconventional diplomacy by the US, including three face-to-face meetings between Donald Trump and Mr Kim.

While the US president has claimed success in stalling Mr Kim’s testing of long-range missiles since 2018, many international experts believe little progress toward denuclearisation has been made.

“We’re really seeing the check come due on Trump’s reality show diplomacy with Kim Jong Un — and it’ll be Joe Biden that’ll have to pick up the tab,” Mr Panda said.

Mr Kim has not joined other autocracies in gloating at the US over the violence that broke out in Washington this week.

But the 37-year-old dictator might later raise Washington’s political tumult to justify distrust of nuclear negotiations with the US or to support China on global governance questions, said Leif-Eric Easley, a North Korea expert at Ewha Womans University in Seoul.

The ruling party congress in Pyongyang was also closely watched for a new five-year economic plan, following Mr Kim’s rare concession in August over failures to achieve long-term development objectives.

The new plan comes as North Korea faces its worst economic crisis in years, battered by sanctions and border closures stemming from the coronavirus, as well as damage from typhoons and flooding.

It sets out goals of greater self-reliance and centralisation but offers little hope of improving the lives of the majority of the country’s 25m people, analysts said.

Peter Ward, a Seoul-based North Korea economy expert with the University of Vienna, said the “anti-market” trend, which has been building for several years, is now reversing tentative steps towards economic freedoms.

“It looks like the re-centralisation of planning, in both the industrial sector and state firms generally. We saw continued talk of restoring the state commercial sector and reasserting control over distribution – which is very concerning,” Mr Ward said.