WASHINGTON • The United States is ready to open investment to North Korea once it has verifiable proof of the Asian nation's denuclearisation, said President Donald Trump's top national security aide.

"We are prepared to open the trade and investment with North Korea as soon as we can," National Security Adviser John Bolton said on ABC's This Week in one of two appearances in political shows yesterday.

Secretary of State Mike Pompeo also spoke of the potential for US investment in the isolated nation.

Before the benefits flow, though,"we want to see the denuclearisation process so completely under way that it is irreversible", said Mr Bolton.

The remarks come ahead of a historic summit between Mr Trump and North Korean leader Kim Jong Un in Singapore on June 12 to pave the way for the latter to give up his nuclear arsenal.

Mr Kim is expected to seek swift relief from severe economic sanctions in exchange for steps to shut down his country's nuclear programme. Washington has insisted that Pyongyang completely abandon its nuclear programme before easing it eases its "maximum pressure campaign" of sanctions and diplomatic isolation.

"He sees the chance of a breakthrough, but I don't think he has stars in his eyes over this," Mr Bolton said of Mr Trump.

US Secretary of State Mike Pompeo said on Fox News Sunday that North Korea would be allowed access to private-sector US capital for infrastructure projects such as an energy grid if "complete, verifiable, irreversible denuclearisation" occurs.

Mr Pompeo also hinted that the US might assure Mr Kim he could stay in power after any deal.

Dialogue brokered by South Korea has seen US-North Korea relations go from the leaders of both countries trading insults and threats of war last year to making plans for the upcoming summit in Singapore.

Mr Kim met Mr Pompeo in Pyongyang last week, and let him take three American prisoners home with him.

The North has scheduled the dismantlement of its nuclear bomb test site for some time between May 23 and 25, to uphold its pledge to discontinue nuclear tests, its state media reported on Saturday.

Pyongyang said it would allow journalists from China, Russia, the US, Britain and South Korea to conduct "on-the-spot coverage" of a ceremony for the dismantling.

Mr Trump welcomed the North Korean announcement. "Thank you, a very smart and gracious gesture!" he tweeted.

Professor Kim Dong Yub of Kyungnam University's Far East Institute said the US and North Korea may have already reached "a certain level of agreement".

"Their agreement could be the US beginning to discuss rewards for North Korea or giving low-level rewards to the country as it begins to take action (for denuclearisation)."

Prof Kim also pointed out that sanctions relief could come as a first step as early as this year, as both leaders could use the political achievement. Mr Trump is facing mid-term congressional elections, and Mr Kim needs to deliver tangible results in boosting the economy with his 2016-2021 economic plan in place.

"The deadline would be 2020 for both countries, before the US holds its next presidential election and North Korea completes its five-year economic plan," Prof Kim said.

Sceptics however, fear that Mr Kim does not really intend to give up his nuclear weapons and is merely trying to soften his image, escape sanctions and make it harder for Mr Trump to threaten military action.

BLOOMBERG, THE KOREA HERALD/ASIA NEWS NETWORK