North Korean leader Kim Jong Un has threatened to expand his nuclear arsenal and develop more sophisticated weapons unless the US ends what he calls its "hostility" to his regime.

Mr Kim's comments during a key meeting of the ruling party were seen as applying pressure on the incoming administration of Joe Biden, who has called Mr Kim a "thug" and has criticised his summits with Donald Trump.

The Korean Central News Agency quoted Mr Kim as saying the "key to establishing new relations between (North Korea) and the United States is whether the United States withdraws its hostile policy".

READ MORE: Kim Jong Un rumours spark succession speculation

Mr Kim said he will not use his nuclear weapons first unless threatened. He also suggested he is open to dialogue if Washington is, but stressed North Korea must further strengthen its military and nuclear capability to cope with intensifying US hostility.
He again called the US his country's "main enemy".

"Whoever takes office in the US, its basic nature and hostile policy will never change," he said.

Mr Biden, who will take office on January 20, is unlikely to hold direct meetings with Mr Kim unless the North Korean leader takes significant denuclearisation steps.

Mr Kim did not cite any specific provocative US actions. North Korea has previously called regular US military drills with South Korea an invasion rehearsal, though the allies have repeatedly denied that.

The North Korean leader listed sophisticated weapons systems he said were under development, including a multi-warhead missile, underwater-launched nuclear missiles, solid-fuelled long-range missiles and spy satellites.

He said Pyongyang must also advance the precision attack capability on targets in 15,000-kilometre (9,320-mile) range - an apparent reference to the US mainland - and develop technology to manufacture smaller nuclear warheads to be mounted on long-range missiles more easily.

READ MORE: Kim Jong Un takes central stage at North Korean military parade

"The reality is that we can achieve peace and prosperity on the Korean peninsula when we constantly build up our national defence and suppress US military threats," Mr Kim said.

It is unclear if North Korea is capable of developing such systems. It is one of the world's most cloistered countries, and estimates on the status of its nuclear and missile programmes vary widely. In 2018, the South Korean government said North Korea was estimated to have up to 60 nuclear weapons.