North Korea said on Thursday that it will never unilaterally give up its nuclear weapons unless the US first removes what Pyongyang called a nuclear threat. The surprisingly blunt statement jars with Seoul's more rosy presentation of the North Korean position and could rattle the already fragile diplomacy between Washington, Seoul and Pyongyang to defuse a nuclear crisis that last year had many fearing war.

The latest from North Korea comes as the US and North Korea struggle over the sequencing of the denuclearisation that Washington wants and the removal of international sanctions desired by Pyongyang. The statement carried by the North's official Korean Central News Agency also raises credibility problems for the liberal South Korean government, which has continuously claimed that North Korean leader Kim Jong-un is genuinely interested in negotiating away his nuclear weapons as Seoul tries to keep alive a positive atmosphere for dialogue.

The North's comments may also be taken up as proof of what many outside skeptics have long said: that Kim will never voluntarily relinquish an arsenal he sees as a stronger guarantee of survival than whatever security assurances the US might provide. The statement suggests that North Korea will demand that the US withdraw or significantly reduce the 28,500 American troops stationed in South Korea, which would be a major sticking point to a potential disarmament deal.

Kim and President Donald Trump met June 12 in Singapore where they issued a vague goal for the 'complete denuclearisation' of the Korean Peninsula without describing when and how it would occur. The leaders are trying to arrange another meeting for early next year.

But North Korea for decades has been pushing a concept of denuclearisation that bears no resemblance to the American definition, with Pyongyang vowing to pursue nuclear development until the United States removes its troops and the nuclear umbrella defending South Korea and Japan.

In Thursday's statement, the North made clear it's sticking to its traditional stance on denuclearisation. It accused Washington of twisting what had been agreed on in Singapore and driving post-summit talks into an impasse.

'The United States must now recognize the accurate meaning of the denuclearization of the Korean Peninsula, and especially, must study geography,' the statement said.

'When we talk about the Korean Peninsula, it includes the territory of our republic and also the entire region of (South Korea) where the United States has placed its invasive force, including nuclear weapons. When we talk about the complete denuclearization of the Korean Peninsula, it means the removal of all sources of nuclear threat, not only from the South and North but also from areas neighboring the Korean Peninsula,' the statement said.

The US removed its tactical nuclear weapons from South Korea in the 1990s.

This June 12, 2018, file photo, shows Donald Trump with Kim Jong-un on Sentosa Island in Singapore. AP

Washington and Seoul did not immediately respond to the North Korean statement.

North Korea's reiteration of its long-standing position on denuclearisation could prove to be a major setback for diplomacy, which was revived early this year following a series of provocative nuclear and missile tests that left Kim and Trump spending most of 2017 exchanging personal insults and war threats. The statement could jeopardise Trump's plan to hold a second summit with Kim early next year as it could be difficult for the US to push negotiations further if the North ties the future of its nukes to the US military presence in the South, analysts said.

South Korean President Moon Jae-in, who met Kim three times this year and lobbied hard for the Trump-Kim meeting, has said that Kim wasn't demanding the withdrawal of US troops from the Korean Peninsula as a precondition for abandoning his nuclear weapons. But Kim has never made such comments in public.

'The blunt statement could be an indicator that the North has no intentions to return to the negotiation table anytime soon,' said Shin Beomchul, a senior analyst at Seoul's Asan Institute for Policy Studies. 'It's clear that the North intends to keep its nukes and turn the diplomatic process into a bilateral arms reduction negotiation with the United States, rather than a process where it unilaterally surrenders its programme.'

The nuclear negotiations between Washington and Pyongyang have stalled since the Trump-Kim meeting. The United States wants North Korea to provide a detailed account of nuclear and missile facilities that would be inspected and dismantled under a potential deal, while the North is insisting that sanctions be lifted first.

The North Korean statement came a day after Stephen Biegun, the Trump administration's special envoy on North Korea, told reporters in South Korea that Washington was reviewing easing travel restrictions on North Korea to facilitate humanitarian shipments to help resolve the impasse in nuclear negotiations.