N. Korea will never fully give up nuclear weapons

North Korea will never completely give up its nuclear weapons, a top defector said ahead of leader landmark summit with US President Donald Trump next month.

The current whirlwind of diplomacy and negotiations will not end with "a sincere and complete disarmament" but with "a reduced North Korean nuclear threat", said Thae Yong-ho, who fled his post as the North's deputy ambassador to Britain in August 2016.

"In the end, North Korea will remain 'a nuclear power packaged as a non-nuclear state'," Thae told the South's Newsis news agency.

His remarks come ahead of an unprecedented summit between Kim and Trump in Singapore on June 12, at which North Korea's nuclear and missile programmes are expected to dominate the agenda.

North and South Korea affirmed their commitment to the goal of denuclearisation of the peninsula at a summit last month, and Pyongyang announced at the weekend it would destroy its only known nuclear test site next week.

South Korean President Moon Jae-in on Monday welcomed the announcement, calling it an "initial step in the complete denuclearisation of North Korea".

But North Korea has not made public what concessions it is offering, and the South's JoongAng Ilbo daily pointed out that it had only invited journalists to witness the operation at the Punggye-ri site.

"It is regrettable that North Korea did not invite nuclear experts to the destruction of the test site," it said in an editorial. "If North Korea has really decided to denuclearise, it has no reason not to invite them."

Pyongyang has said it does not need nuclear weapons if the security of its regime is guaranteed.

US Secretary of State Mike Pompeo, who has met Kim twice, said he was "convinced" the North Korean leader shared US goals, and promised security assurances and bountiful American investment in the isolated nation.

"Those are the kind of things that, if we get what it is the President has demanded -– the complete, verifiable, irreversible denuclearisation (CVID) of North Korea -– that the American people will offer in spades," Pompeo said on Fox News Sunday.

But verification will be key.

And Thae, one of the highest-ranking officials to have defected in recent years, said: "North Korea will argue that the process of nuclear disarmament will lead to the collapse of North Korea and oppose CVID."

At a party meeting last month Kim proclaimed the development of the North's nuclear force was complete and promised no more nuclear or missile tests. He called its arsenal "a powerful treasured sword for defending peace".

"Giving it up soon after Kim Jong Un himself labelled it the 'treasured sword for defending peace' and a firm guarantee for the future? It can never happen," said Thae, who now lives in South Korea and whose memoir hit the shelves Monday.

'Peace gestures'

Tensions on and around the peninsula had been mounting for years as Pyongyang's nuclear and ballistic missile programmes saw it subjected to increasingly strict sanctions by the UN Security Council, the US, EU, South Korea and others.

Trump last year threatened the North with "fire and fury".

But since the Winter Olympics in the South, Pyongyang and Washington have agreed to their unprecedented meeting.

Kim has also twice visited China after failing to pay his respects to President Xi Jinping in the six years since he inherited power from his father. He also met the South's President Moon Jae-in in the Demilitarized Zone that divides their countries.

On Monday Japanese media said an unidentified high-level North Korean official arrived in Beijing, reportedly to brief China about Pompeo's recent visit to Pyongyang. He returned with three freed US detainees, the latest in the North's diplomatic overtures.

Pyongyang's sudden change in attitude was probably driven by the mounting international sanctions, which have included measures hitting sectors including coal, fish, textiles and overseas workers, Thae said.

But it had a long history of making overtures that ultimately came to nothing, he warned.

"North Korea's diplomacy has always been a repeat of hardline and appeasement," Thae said.

"It is North Korea's diplomatic tactic to push the situation to extreme confrontation and suddenly send peace gestures."