The two leaders are due to meet next week in Hanoi after their groundbreaking first summit in Singapore last June, which produced a vague statement on the "denuclearisation of the Korean peninsula".

Senior officials from Washington and Pyongyang are holding preparatory talks in Hanoi -- which are expected to be largely focused on establishing the agenda for the summit.

Stephen Biegun, the US Special Representative on North Korea who is leading the American delegation, acknowledged last month that Pyongyang and Washington did not have a "shared agreement of what denuclearisation entails".

The lack of progress since the first summit has fuelled scepticism in Washington over the North's intentions, with Trump's own intelligence chief saying Pyongyang was unlikely to completely give up its weapons programme.

But in a sharply-worded commentary issued Sunday, the North's official Korean Central News Agency slammed US critics and urged the Trump administration to seize "the rare historic opportunity".

"The US administration must not forget last year's lesson when it plunged the bilateral negotiations into a stalemate, being swayed by the opponent forces," it said.

"If the upcoming DPRK-US negotiations end without results as wished by the opponent forces, the US people will never be cleared of the security threats," it added.

Pyongyang is seeking relief from punishing UN sanctions and rejects demands for what it calls its "unilateral" disarmament.

Washington insists that the measures must stay in place until North Korea gives up its nuclear arsenal.

Experts say tangible progress is needed in Hanoi to avoid the talks being dismissed as a publicity stunt.