But he also criticised the US for undermining confidence in the process: “What is alarming, however, is the insistent moves manifested within the US to go back to the old, far from its leader’s intention.”

“As long as the US does not show in practice its strong will to remove our concerns, there will be no case whereby we will move forward first unilaterally,” Ri added.

His comments came after Pompeo said at the same forum that he was emphasising to countries “the importance of maintaining diplomatic and economic pressure on North Korea”, while adding that he was “optimistic” about the prospects for progress when it came to North Korean denuclearisation.

At the June 12 historic talks in Singapore, Kim signed up to a vague commitment to “denuclearisation of the Korean Peninsula” – a far cry from long-standing US demands for complete, verifiable and irreversible disarmament.

Since the agreement, Pyongyang had taken “goodwill measures”, including a halt on nuclear and missile tests and “dismantling a nuclear test ground”, Ri said, according to a statement.

He said the US “is raising its voice louder for maintaining the sanctions against the DPRK,” referring to the initials of North Korea’s official name.

Pompeo still ‘optimistic’

Saturday’s forum in Singapore, hosted by the Association of Southeast Asian Nations (ASEAN), brings together top diplomats from 26 countries and the European Union for talks on political and security issues in the Asia-Pacific.

As well as the US and North Korea, it includes foreign ministers from China, Russia, South Korea and Japan, all countries traditionally involved in efforts to curtail North Korea’s nuclear ambition.

At the meeting, the US delegation also delivered a letter from Trump intended for Kim, by passing it to Ri, Pompeo said in a tweet.

It was Trump’s reply to a letter he received from Kim earlier this week, he said.

While US officials have publicly been optimistic about the agreement, Pyongyang appears to have made little substantial progress and concerns have been growing that some UN member states have been easing sanctions.

A new UN report showed Pyongyang was continuing with its nuclear and missile programme, and evading sanctions through ship-to-ship oil transfers.

On Saturday, Pompeo briefly met North Korea’s foreign minister, greeting him at a joint photo of ministers, with the pair shaking hands, smiling and exchanging some words.

While the encounter was brief, Department of State spokeswoman Heather Nauert described it as a “step in the right direction” given where US-North Korea relations were a year ago, as tensions soared due to North Korea’s weapons tests.