A senior North Korean official has dismissed remarks by US Vice-President Mike Pence as "stupid", casting further uncertainty about a planned meeting between the two countries' leaders.
Choe Son-hui said Pyongyang would not "beg" for dialogue and warned of a "nuclear showdown" if diplomacy failed.
In recent days, both sides have said that the 12 June Trump-Kim summit could be delayed or even called off.
Pyongyang has insisted it would not give up nuclear weapons unilaterally.
US President Donald Trump on Tuesday said that it was the North that had to meet the conditions for the talks to go ahead.
'Impudent'
Choe Son-hui has been involved in several diplomatic interactions with the US over the past decade.
Her latest comments came days after Mr Pence warned that North Korea "may end like Libya" – where then-leader Muammar Gaddafi was killed by rebels in 2011 after renouncing nuclear weapons eight years earlier.
In an article carried by the state news agency KCNA on Thursday, Ms Choe said Mr Pence had made "unbridled and impudent remarks".
She added: "As a person involved in US affairs, I cannot suppress my surprise at such ignorant and stupid remarks gushing from the mouth of the US vice-president.
"Whether the US will meet us at a meeting room or encounter us at nuclear-to-nuclear showdown is entirely dependent upon the decision and behaviour of the United States."
US National Security Adviser John Bolton also angered North Korea last week by saying it could follow a "Libya model" of verifiable denuclearisation.
That led to North Korea's vice-foreign minister threatening to pull out of the Trump-Kim summit.
Meanwhile North Korea is pressing ahead with plans to dismantle its only nuclear testing facility later this week.
The Punggye-ri site is located in a remote part of the north-west of the country. A group of international journalists, who have been invited to observe the event, are on their way there.
'Careful diplomacy requires careful messaging'
Analysis from Laura Bicker, BBC News, Seoul
So we are back to name calling and threats of nuclear war – just weeks before the planned summit.
The messenger is a powerful figure in North Korean politics. She's one of Kim Jong-un's top aides, so this statement will have been sanctioned by the chairman himself.
Some may say this is a typical Pyongyang power play. But it was also so avoidable.
North Korea had made it clear last week that mentioning the Libyan model of denuclearisation touched a nerve. Firstly because the Gaddafi regime collapsed and he was killed, but also because the North believe its weapons programme is far more advanced than Libya's ever was.
So to even mention the two countries in the same context will be a grave insult and Pyongyang may feel that Washington is not showing it the respect it deserves.
The US had been warned, and yet Mr Pence decided to repeat the comparison anyway. Careful diplomacy requires careful messaging and careful language, and North Korea clearly feels the Trump administration has shown a lack of discipline in this regard.
It is interesting that Pyongyang decided not to target Donald Trump who also made similar remarks. Aiming the insults at those around the president rather than Mr Trump himself may suggest North Korea is not ready to throw away the prospect of a summit quite yet./BBC