Kim Jong-un used a New Year message on Monday to say that North Korea would mass-produce nuclear warheads and the missiles that carry them, suggesting he would accelerate a weapons programme that has stoked international tensions.
Mr Kim, who said that he always had a nuclear launch button on his desk, has presided over several missile tests in recent months and the North's sixth and most powerful nuclear test — which it said was a hydrogen bomb — in September.
"We must mass-produce nuclear warheads and ballistic missiles and speed up their deployment," said Mr Kim in his annual address to the nation.
He reiterated his claims that North Korea had achieved its goal of becoming a nuclear power but insisted its expansion of the weapons programme was a defensive measure.
"We should always keep readiness to take immediate nuclear counter-attacks against the enemy's scheme for a nuclear war."
Pyongyang ramped up its efforts to become a nuclear power in 2017, despite international sanctions and increasingly bellicose rhetoric from the United States.
The North claims it needs nuclear weapons to protect itself from a hostile Washington and has strived to create a warhead capable of targeting the US mainland.
US president Donald Trump has responded to each test with his own amplified declarations, threatening to "totally destroy" Pyongyang and taunting Mr Kim, saying the North Korean leader was on "a suicide mission".
But far from persuading Mr Kim to give up his nuclear drive, analysts said Mr Trump's tough talk may have prompted the North Korean leader to push through with his quest.
"[The North] can cope with any kind of nuclear threats from the US and has a strong nuclear deterrence that is able to prevent the US from playing with fire," Mr Kim said.
"The nuclear button is always on my table. The US must realise this is not blackmail, but reality."
Mr Kim's comments came after a former senior US military officer warned that the Trump presidency had helped create "an incredibly dangerous climate".
"We're actually closer, in my view, to a nuclear war with North Korea and in that region than we have ever been," said Mike Mullen, a former chairman of the US joint chiefs of staff, in an interview on ABC's This Week on Sunday.
When asked for a response to Mr Kim's claim that he had a nuclear button on his desk, Mr Trump said: "We'll see, we'll see", in comments to reporters during the New Year's Eve party at his Mar-a-Lago resort in Florida.
Pyongyang regards American military activities in the region — such as the joint drills it holds with the South — as a precursor to invasion.
It has rattled the international community by testing increasingly longer-range intercontinental ballistic missiles (ICBMs) throughout 2017.
But any military intervention by the US could escalate into a conflict that would threaten the lives of millions.
Critics said Pyongyang wants to forcibly reunify the peninsula — divided by a demilitarised zone since the ceasefire of the 1950-1953 Korean war.
But Mr Kim also sugared his speech on Monday with a conciliatory tone towards Seoul, indicating for the first time that the North is considering taking part in the South's Winter Olympics next month.
"[The Olympics] will serve as a good chance to display our Korean people's grace towards the world and we sincerely hope the Games will be a success," Mr Kim said, urging the South to cease its "nuclear war exercise" with the US.
At a time when the risk of a US pre-emptive strike is "higher than ever", Koh Yu-hwan, political science professor at Dongguk University, said the speech indicated Mr Kim was using the Olympics gesture as a means to "shift from confrontation to peaceful co-existence with the United States".
"When he said a nuclear launch button is always on his desk, he is hinting it is not necessary for the North to stage nuclear or ICBM tests in the foreseeable future," he told AFP, adding that he believed Mr Kim also wanted to build "massive nuclear retaliation capabilities".
In December, the UN Security Council unanimously passed more US-drafted sanctions against Pyongyang, restricting oil supplies vital for the impoverished state.
The third raft of sanctions imposed last year, which the North criticised as an "act of war", also received the backing of China — the country's sole major ally and economic lifeline.
Observers said Washington must open talks with the North to defuse tensions — but that remains a challenge.
Pyongyang has always said it will only deal with the US from a position of equality as a nuclear state.
Washington has long insisted that it will not accept a nuclear-armed North and Pyongyang must embark on a path towards nuclear disarmament before any talks.