Trump: "N Korea could become “great power” without nuclear weapons"

North Korea could become one of the world's "great economic powers" if it relinquishes its nuclear weapons, US President Donald Trump has said.

Writing on Twitter, Trump said the nation had "more potential for rapid growth than any other".

His comments came hours after his secretary of state Mike Pompeo said Pyongyang remains a nuclear threat.

Trump will meet North Korean leader Kim Jong-un for the second time on the 27-28 February in Hanoi, Vietnam.

The Vietnam summit is a follow-up to a meeting in Singapore last June which signaled a dramatic reset in relations between two leaders who had been spent previous months saber-rattling and trading insults.

Although that meeting led to little concrete progress in Trump's demands for North Korea to end its nuclear weapons programme, the US leader has changed his tune towards a rival he once ridiculed as "rocket man".

While his top diplomat Mike Pompeo tempered expectations about what could be achieved in Hanoi, Trump said North Korea could become one of the world's "great economic powers" if it relinquished its nuclear arsenal.

"Chairman Kim realizes, perhaps better than anyone else, that without nuclear weapons, his country could fast become one of the great economic powers anywhere in the world," Trump wrote on Twitter.

But Pompeo said North Korea remained a nuclear threat and that while internationally-backed sanctions had helped build pressure on persuading North Korea to denuclearise, it was "a complicated process" and there may have to be another summit after Vietnam.

"We may not get everything done this week. We hope we'll make a substantial step along the way," he told Fox News.

"I hope we can make a real substantive step forward (on denuclearisation) this week. It may not happen but I hope that it will."

While Singapore produced a vaguely worded agreement on denuclearisation, progress has since stalled, with the two sides disagreeing over what the agreement meant.

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