North Korea has lashed out at the US for continuing to push for sanctions enforcement.
Pyongyang said there would be no progress towards denuclearisation if the US followed an “outdated script”.
It accused US negotiators of going against the intentions of President Donald Trump and the spirit of the summit in Singapore.
Mr Trump and North Korean leader Kim Jong-un agreed at the June meeting to work towards denuclearisation.
Read: US migrants: Judge orders deportation plane turnaround
But the details of that process remain vague – North Korea did not commit to unilaterally give up its nuclear weapons and the UN says its nuclear programme is continuing.
The US has insisted it is vital to maintain diplomatic and economic pressure on the North.
“As long as the US denies even the basic decorum for its dialogue partner and clings to the outdated acting script which the previous administrations have all tried and failed, one cannot expect any progress in the implementation of the joint statement including the denuclearisation,” North Korea’s foreign ministry said on Thursday.
The warnings come just days after North Korea’s foreign minister called US actions “alarming”.
Last month, North Korea accused the US of using “gangster-like” tactics in the negotiations.
‘Waiting for a boiled egg to hatch’
The latest statement by the North’s foreign ministry also accused US officials of “going against the intention of President Trump” by “making baseless allegations against us and making desperate attempts at intensifying the international sanctions and pressure”.
It said “expecting any result, while insulting the dialogue partner” was “a foolish act that amounts to waiting to see a boiled egg hatch out”.
The fresh anger out of Pyongyang comes as top diplomats from the US have strongly criticised the North’s commitment to denuclearisation.
National security adviser John Bolton earlier this week said North Korea had not begun the progress, while US envoy to the UN, Nikki Haley, said Washington was “not willing to wait for too long” for the North.
Read: Costa Rica Supreme Court rules against same-sex marriage ban
Pyongyang’s Foreign Minister Ri Yong-ho is currently on a visit to Iran where President Hassan Rouhani warned the US could not be trusted after Tehran’s experience of having the Trump administration tear up an Obama-era deal to ease sanctions.
According to Iranian media, Mr Ri said his country would seek to retain its nuclear skills for when the US would revert to a more aggressive position against Pyongyang.
“Since we know that the US will never give up its hostile policy toward us, we will hold onto our nuclear knowledge,” he was quoted by local media.