North Korea's foreign minister has called US actions "alarming" as tensions over the North's nuclear programme again flared.
Ri Yong-ho was responding to comments by the US Secretary of State Mike Pompeo urging other countries to keep up sanctions pressure on Pyongyang.
A landmark summit between the US and North Korea in June saw the North agree to work towards denuclearisation.
But details remain vague and the UN says its nuclear programme continues.
At a regional forum in Singapore, Mr Pompeo said it was important to maintain "diplomatic and economic pressure" on North Korea to achieve "the final, fully verified denuclearisation".
Pyongyang is currently under a range of international and US sanctions over its nuclear programme and missile tests.
Mr Pompeo said he expected all nations to abide by the sanctions, singling out Russia amid reports that it had potentially violated them by allowing thousands of North Korean labourers into the country. Russia has denied this.
In response, Mr Ri said that North Korea "stands firm" in its commitment made at the June summit between US President Donald Trump and North Korean leader Kim Jong-un.
He added: "What is alarming however is the insistent moves manifested within the US to go back to the old, far from its leader's intention".
Mr Ri and Mr Pompeo only met face-to-face briefly, exchanging smiles, handshakes and a few brief words.
Also at Saturday's meeting, the US delegation delivered a letter from Mr Trump for Mr Kim. It is unclear what it contained.