WASHINGTON - Real progress has been made in talks between the United States and North Korea ahead of a proposed summit in Singapore, US Secretary of State Mike Pompeo told journalists in New York after a second meeting with Mr Kim Yong Chol, right hand man to North Korean leader Kim Jong Un and the senior most official from that country to visit the US in almost 20 years.

Mr Pompeo confirmed that Mr Kim Yong Chol will travel to Washington on Friday (June 1) to deliver a personal letter from North Korean leader Kim Jong Un to President Donald Trump.

Mr Pompeo stopped short of confirming that the on-again, off-again summit panned for June 12 is finally set. Asked if that would become clear on Friday he said "I don't know."

But he added: "We've made real progress in the last 72 hours towards setting the conditions."

"The conditions are putting President Trump and Chairman Kim Jong Un in a place where we think there can be real progress made by the two of them meeting."

It would do no good if they were in a place in which there was no real opportunity in having them meet, he said.

Mr Trump's objective remained the complete, verifiable and irreversible denuclearisation of the Korean peninsula, he said. That meant all elements of its nuclear programme.

The United States also understood the concerns of its allies Japan and South Korea, he said."We understand their concerns, we understand the risks that can be posed to them, and any agreement that we reach will provide an outcome that each of those countries can sign on to as well," he said.

"The effort now is to come to a set of understandings to convince the North Koreans... that in fact the real threat is their holding on to their nuclear weapons and not the converse; we've had lots of conversation around that," Mr Pompeo said.

"The true test of course comes when we actually achieve this, but many conversations have been had about... what the path might be so we can achieve the denuclearisation the world demands of North Korea, and the security assurances that would be required for them to allow us to achieve that."

The proposed summit "offers a historic opening for President Trump and Chairman Kim to boldly lead the United State and the DPRK (the Democratic People's Republic of Korea, which is the country's official name) into a new era of peace, prosperity and security," he said.

"Our two countries face a pivotal moment in our relationship in which it would be nothing short of tragic to let this opportunity go to waste. We sincerely hope that Chairman Kim Jong Un shares this positive vision for the future."

"I have had the chance to meet Chairman Kim Jong Un twice now and Kim Yong Chol three times and spent a great deal of time with each of them," he said. "I believe they are contemplating a path forward, they can make a strategic shift, one which their country has not been prepared to make before."

But he cautioned that the process would not be straightforward. Some roadblocks may even be perceived as insurmountable. "They have to choose a path that is fundamentally different than the one their country has proceeded on for decades," he said.

"This is going to be a process that will take days and weeks to work our way through," he said.

"There will be tough moments, there will be difficult times. I've had some difficult conversation with them as well; they've given it right back to me too. One ought not to be either surprised or frightened or deterred by moments when it looks like there are things that can't be bridged; our mission is to bridge them."

"We expect both leaders to enter the summit in Singapore, if it proceeds, with their eyes wide open… and a clear understanding of the possibilities for the future," he said. "If these talks are successful it will truly be historical."

"It will take bold leadership from Kim Jong Un to seize this once in a lifetime opportunity," he said. "President Trump and I believe Chairman Kim is the kind of leader who can make those kinds of decisions and in the coming weeks and months we will have the opportunity to test whether or not this is the case."