The North has portrayed the destruction on the test site as a goodwill gesture ahead of planned 12 June summit between Kim Jong-un and Trump in Singapore.
"I did a great service to this country by firing James Comey", Mr. Trump said Wednesday. The president spent much of his morning tweeting about the Federal Bureau of Investigation allegedly spying on his campaign, after multiple outlets reported the Federal Bureau of Investigation utilized a retired professor to meet with Trump campaign officials in 2016.
It follows a historic meeting between the leaders of the Koreas in April.
But there has been increasing pessimism about the meeting after North Korea scrapped the inter-Korean talks and threatened to do the same for the Kim-Trump summit in protest at the South Korea-US military drills and what it calls Washington's push for "one-sided" disarmament.
Worldwide journalists on Wednesday set out on an arduous journey to witness the dismantlement of North Korea's nuclear test site, Punggye-ri - an event that experts predict will be more about PR than substance.
"The maximum pressure campaign of diplomatic and economic sanctions is bearing fruit with the historic meeting set to take place on June 12th", and was supported by allies, Pompeo said.
"That decision will ultimately be up to Chairman Kim", he said.
Pompeo said that "if we can get America's interests safe and secure we are prepared to do a great deal", including security assurances for Kim.
Secretary of State Mike Pompeo says the Trump administration will walk away from talks with North Korea if the "right deal" is not on the table for negotiation.
Pompeo, who was director of the Central Intelligence Agency before becoming secretary of state in April when Trump fired Rex Tillerson, has met twice with Kim in Pyongyang. "They must know what price they will be made to pay", the commentary said, using the North's traditional lowercase "s" when describing the South.
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The North also threatened to abandon the planned Mr Trump-Kim meeting over U.S. insistence on rapidly denuclearising the peninsula, issuing a harshly worded statement that the White House dismissed as a negotiating ploy.
That was a reference to Libya's former leader, Muammar Gaddafi, who agreed to give up nuclear weapons in 2003 and was later killed by Western-backed rebels.
Moon's White House visit was meant to be a fine-tuning of the US and South Korean strategy for dealing with North Korean leader Kim Jong Un.
"That model would take place if we don't make a deal, most likely".
"We're continuing to do our work and lay the foundation for a successful meeting", Pompeo told reporters.
Why does the Singapore summit matter so much?
Trump suggested the summit could be delayed rather than canceled: "It may not work out for June 12, but there is a good chance that we'll have the meeting".
Mr Trump accepted North Korea's invitation for direct talks after more than a year of heated rhetoric and with global concern that hostilities might escalate into military confrontation.
According to the report, Kim is less concerned about meeting Trump than he is about what might happen at home in Pyongyang while he's gone.
In a surprise announcement Pyongyang said earlier this month that it planned to "completely" destroy the Punggye-ri facility in the country's northeast, a move welcomed by Washington and Seoul. But whereas Trump dreads political embarrassment, Kim has more existential fears.