Trump and Kim face unanswered questions in Vietnam

US President Donald Trump and North Korean leader Kim Jong Un meet in Hanoi this week, faced with putting meat on the bones of the vaguely worded declaration that emerged from their historic first summit in Singapore.

That encounter -- the first-ever between the leaders of the US and North Korea -- left many ambiguities on the key question of denuclearisation and analysts say clearer answers need to emerge in the Vietnamese capital.

At the June meeting, Kim pledged to "work towards complete denuclearisation of the Korean peninsula" but the lack of progress since then has drawn criticism that the leaders were only after headlines and short-term gains.

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

The United States has repeatedly demanded the North give up its nuclear arsenal in a final, fully verifiable way.

Pyongyang sees denuclearisation more broadly, seeking an end to sanctions and what it sees as US threats -- usually including the American military presence in the South, and sometimes in the wider region.

"The ambiguity and obscurity of the term denuclearisation only exacerbates the scepticism about both the US and North Korean commitments to denuclearisation," wrote Shin Gi-wook, director of the Korea Program at Stanford University.

Trump has employed both carrots and sticks to pursue North Korea's denuclearisation, praising the regime's potential as a "great economic powerhouse" but saying tough sanctions will remain until it takes a "meaningful" step.

Pyongyang insists it has already done so, by not testing ballistic missiles or nuclear weapons for more than a year, and blowing up the entrances to its atomic test site.

But at the same time, North Korea says it has completed the development of its arsenal and the facilities are no longer needed.

Diplomats in Pyongyang say authorities have emphasised Kim's demand in his New Year speech that the US must respond with "trustworthy measures and corresponding practical actions".

The two need to take "at least one step forward on denuclearisation" in Hanoi, said Harry Kazianis of the Center for the National Interest, adding: "Nothing would be worse than for either side to come out of the meeting as if it was a waste of time."