Kim Jong-un has boasted of having a 'nuclear button' on his desk as he warned the US that the entire country is within range of his weapons.

The North Korean dictator also announced plans to start mass-producing nuclear warheads as he delivered a televised New Year's Day speech.

The tyrant warned America that it can 'never start a war against me and our country' and insisted his nukes are now a reality, not a threat.

'We must mass-produce nuclear warheads and ballistic missiles and speed up their deployment,' said Kim in his annual address to the nation.

Kim Jong Un has boasted of having a 'nuclear button' on his desk as he warned the US that the entire country is within range of his weapons

'We should always keep readiness to take immediate nuclear counter-attacks against the enemy's scheme for a nuclear war.

'The U.S. should know that the button for nuclear weapons is on my table. This is reality, not a threat. The entire area of the U.S. mainland is within our nuclear strike range. ... The United States can never start a war against me and our country.'

However, Kim also called for improved relations with the South, an idea mentioned in speeches more often than it is met.

He said the Pyeongchang Winter Olympics would be a good opportunity to showcase the status of the Korean nation.

He said the North and South could meet urgently to discuss the North sending a delegation.

'The Winter Olympic games that will be held soon in the South will be a good opportunity to display the status of the Korean nation and we sincerely wish that the event will be held with good results,' he said'.

The New Year's address is an annual event in the North and is watched closely for indications of the direction and priorities Kim may adopt in the year ahead.

Fireworks are seen above the Taedong River during New Year celebrations as visitors pose for a photo in front of an ice sculpture of an intercontinental ballistic missile at the Pyongyang Ice Sculpture Festival in Kim Il Sung Square in Pyongyang, North Korea

Kim Jong-un warned in his New Year's Day speech: 'The entire United States is within range of our nuclear weapons, and a nuclear button is always on my desk

A group of men stand before an ice sculpture depicting a Hwasong-15 intercontinental ballistic missile (ICBM) at the Pyongyang Ice Sculpture Festival on New Year's Eve

Children pose for a photo before an ice sculpture of an ICBM and self-propelled launcher at the festival on Kim Il Sung Square

Children stand before an ice sculpture at the Pyongyang Ice Sculpture Festival, marking the New Year on Kim Il Sung Square

The day before, many of the isolated nation's citizens spent New Year's Eve at the Pyongyang Ice Sculpture Festival on Kim Il Sung Square.

There, visitors took pictures with sculptures inspired by the North Korean leader's determination to build a nuclear arsenal.

Taking pride of place at the festival was a massive ice sculpture depicting a Hwasong-15 intercontinental ballistic missile (ICBM).

Earlier on Sunday, Mike Mullen, a former top US military officer, warned the US is closer than it has ever been to nuclear war with North Korea.

Adm Mullen, a former chairman of the joint chiefs of staff, attributed the rising danger to Donald Trump's 'incredibly disruptive' presidency.

'And in my view, an incredibly dangerous climate exists out there in that uncertainty with how this all ends up,' he said on ABC's 'This Week.' 'One in particular that is top of the list is North Korea.'

'We're actually closer, in my view, to a nuclear war with North Korea and in that region than we have ever been,' he said, adding, 'I don't see the opportunities to solve this diplomatically at this particular point.'

This photo taken on November 29, 2017 and released on November 30, 2017 by North Korea's official Korean Central News Agency shows launching of the Hwasong-15 missile which is capable of reaching all parts of the US.

Mullen, who served as the top US military adviser to both presidents George W. Bush and Barack Obama, questioned whether Trump can be constrained by Defense Secretary Jim Mattis, National Security Adviser H.R. McMaster or White House Chief of Staff John Kelly.

'Will he follow through on his rhetoric? Or will we actually be able to get to a situation where it could be solved peacefully?' Mullen asked.

'I'm just more inclined to see over time that the rhetoric seems to be where the president is, and that will limit the constraining ability that both Jim Mattis and H.R. McMaster and John Kelly have,' he said.

Trump warned in a speech to the UN General Assembly in September that the United States 'will have no choice but to totally destroy North Korea' if forced to defend itself or its allies.

In August, he vowed to unleash 'fire and fury' on North Korea if it continued to threaten the United States or its allies.

Pyongyang conducted its sixth nuclear test September 3 and, despite escalating sanctions, on Nov. 28 it test-launched an intercontinental missile capable of striking the United States.

Republican Senator Lindsey Graham, who warned Sunday of a sharp increase in the risk of pre-emptive attack if North Korea conducts any more tests, said Trump had decided early on to deny North Korea the capability to strike the United States with a nuclear-tipped missile.

'2018 will be a year of opportunity and extreme danger,' Graham said on CBS's 'Face the Nation.'

'Now, the Iranians are watching the way he engages with North Korea, and vice versa. So we've got a chance here to deliver some fatal blows to really bad actors in 2018. But if we blink, God help us all.'