North Korean leader Kim Jong-un said that his country would soon unveil a new strategic weapon as it bolsters its nuclear deterrent in the face of "gangster-like" US pressure.
Mr Kim accused the Trump administration of dragging its feet in nuclear negotiations and threatened "shocking" action.
He said North Korea would no longer be obligated to maintain a self-imposed moratorium on the testing of nuclear weapons and intercontinental ballistic missiles, which President Donald Trump has touted as a major diplomatic accomplishment.
Mr Kim, however, gave no clear indication that the restarting of such tests was imminent and seemed to leave the door open for eventual negotiations.
Mr Kim's comments during a four-day plenary meeting of the Workers' Party's Central Committee come as talks falter between Washington and Pyongyang over disagreements involving disarmament steps and the removal of sanctions imposed on North Korea.
The prolonged standstill has dimmed hopes for achieving a full and verifiable denuclearisation of the country through diplomacy.
Mr Kim declared that North Korea would not give up its security for economic benefits in the face of what he described as increasing US hostility and nuclear threats, the Korean Central News Agency said on Wednesday.
The agency reported that Mr Kim as saying North Korea would "never allow the impudent US to abuse the DPRK-US dialogue for meeting its sordid aim but will shift to a shocking actual action to make it pay for the pains sustained by our people so far and for the development so far restrained".
The agency referred to North Korea by its formal name, the Democratic People's Republic of Korea.
Mr Kim also said that "if the US persists in its hostile policy towards the DPRK, there will never be the denuclearisation on the Korean Peninsula and the DPRK will steadily develop necessary and prerequisite strategic weapons for the security of the state until the US rolls back its hostile policy".
In an interview with CBS News, US Secretary of State Mike Pompeo said it would be "deeply disappointing" if Mr Kim reneged on his commitment to pause nuclear and long-range missile tests.
“He made those commitments to President Trump in exchange for President Trump agreeing not to conduct large-scale military exercises,” Mr Pompeo said.
“We’ve lived up to our commitments. We continue to hold out hope that he’ll live up to his as well.”
Mr Trump also urged Mr Kim to stick to his alleged commitment to denuclearise.
After their first summit in Singapore in June 2018, the leaders issued a vague aspirational goal on a nuclear-free Korean Peninsula without when and how it would occur.
“Look, he likes me, I like him, we get along,” Mr Trump said on Tuesday night.
“But he did sign a contract, he did sign an agreement talking about denuclearisation … I think he’s a man of his word so we’re going to find out, but I think he’s a man of his word.”
North Korea for decades has pushed a concept of denuclearisation that bears no resemblance to the American definition, with Pyongyang vowing to pursue nuclear development until the US removes its troops and the nuclear umbrella defending South Korea and Japan.
The KCNA report was vague about the new strategic weapon the country would reveal soon.
North Korean announced in December that it performed two "crucial" tests at its long-range rocket launch site that would further strengthen its nuclear deterrent.
This prompted speculation that it was developing a new ICBM or planning a satellite launch that could help advance its missile technologies.
North Korea has held to its self-imposed moratorium since 2018, though last year it ended a 17-month pause in ballistic activity by testing several solid-fuel weapons that potentially expanded its capabilities to strike targets in South Korea and Japan, including US military bases there.
Mr Kim said North Korea's efforts to bolster its deterrent would be "properly co-ordinated" depending on future US attitudes.
He also said that the more Washington stalls "the more helpless it will find itself before the might of the Democratic People's Republic of Korea getting stronger beyond prediction."
Some experts said North Korea will avoid serious negotiations in the coming months as it watches how Mr Trump's impending impeachment trial over his dealings with Ukraine affects US presidential elections in November.
Mr Kim said there were no longer grounds for North Korea to be "unilaterally bound" to its moratorium, criticising the US for expanding sanctions, continuing military exercises with South Korea and providing Seoul with advanced weaponry.
The allies scaled down major military exercises since 2018 to create space for diplomacy, but North Korea considers such drills to be rehearsals for an invasion and views even the smaller drills as breaching agreements between the leaders.
North Korea also criticised the allies over South Korea's recent acquisition of advanced F-35 fighter jets from the US.
Mr Kim and Mr Trump met three times since June 2018, but negotiations faltered since the collapse of their second summit in Hanoi, Vietnam, last February, after the US rejected demands for broad sanctions relief in exchange for a partial surrender of North Korea's nuclear capabilities.
The KCNA report came hours before North Korean state TV had been expected to broadcast Mr Kim’s New Year’s speech, which he has annually used to announce major changes in security and economic policies.
But the expected speech was replaced with the lengthy report on Mr Kim's comments from the Workers' Party meeting that ended on Tuesday.
In his New Year's Eve speech, Mr Kim said he would seek a "new way" if Washington persisted with sanctions and pressure.
After the Hanoi summit, Mr Kim demanded that Washington come up with new proposals by the end of 2019 to salvage the negotiations.
The Trump administration, which sees economic pressure as its main leverage with Pyongyang, rejected his end-of-year deadline and urged North Korea to return to negotiations.
Mr Kim's comments indicated North Korea's "new way" may look very much like the old one – a determination to wait out sanctions and pressure, which will possibly weaken over time, while patiently cementing the country's status as a nuclear weapons state.
He called for his people to stay resilient in a struggle for economic "self-reliance," doubling down on previous government claims that North Korea could succeed in domestically driven development despite the punitive measures and restrictions imposed on its broken economy.
But Mr Kim also lamented unmet goals in development objectives laid out in 2019, calling for significant improvements in agricultural production and the removal of unspecified "evil practices and stagnation" across industries that include coal mining, electricity production, machinery and railway transport.
He said if the country does not "spur to the struggle for bolstering the power for self-development while waiting for the lift of sanctions, the enemies' reactionary offensive will get fiercer to check our advance," KCNA reported.
