US President Donald Trump has called off next month's summit with North Korea's Kim Jong Un, calling the cancellation a "tremendous setback" for peace.
He also stressed the US military is ready to respond to any "foolish or reckless acts" by the North.
Mr Trump first announced his decision in a letter to Mr Kim released by the White House, in which he cited "tremendous anger and open hostility" in a recent statement by the North, adding that it was "inappropriate, at this time, to have this long-planned meeting".
Speaking at the White House later, Mr Trump said a "maximum pressure campaign" will continue against North Korea and that he was "waiting" should Mr Kim choose to engage in "constructive" actions.
He added that it was "possible that the existing summit could take place or a summit at some later date".
The abrupt cancellation of the June 12 meeting withdraws the US for now from an unprecedented summit that offered the prospect of a historic nuclear peace treaty or an epic diplomatic failure.
No sitting American president has ever met with a North Korea leader.
In the North Korean statement that Mr Trump cited, a top Foreign Ministry official referred to Vice President Mike Pence as a "political dummy" for his comments on the North and said it was up to the US whether they will "meet us at a meeting room or encounter us at nuclear-to-nuclear showdown".
Mr Trump said the world was losing a "great opportunity for lasting peace and great prosperity and wealth".
But he left the door open to the chance that the summit could yet be rescheduled, saying: "If you change your mind having to do with this most important summit, please do not hesitate to call me or write."
One US official said the decision to call off the summit was made on Thursday morning in response to the statement disparaging Mr Pence and threatening nuclear war.
A White House official said it was incorrect to focus solely on the "dummy" comment, saying that the nuclear threats meant that no summit could be successful under such circumstances.
US secretary of state Mike Pompeo said North Korea had not responded to repeated requests from US officials to discuss logistics for the summit.
He told the Senate foreign relations committee the lack of responses was an additional reason for Mr Trump's decision.
Mr Pompeo said the North's attitude had changed markedly since he returned from a trip to Pyongyang earlier this month during which he met with Mr Kim and oversaw the release of three Americans being held there.
South Korean President Moon Jae-in played a major role in planning for the summit and sought to keep it on the rails in a visit to the White House this week.
His office said that it was trying to work out Mr Trump's intentions in cancelling the summit.
Mr Pompeo, asked about a report that the South had not been informed before the president's letter was made public, said simply: "We are locked in to the Republic of Korea. We are in lockstep with them."
The cancellation came shortly after Mr Kim made good on his promise to demolish his country's nuclear test site, which was formally closed in a series of huge explosions on Thursday as a group of foreign journalists looked on.
The explosions at the test site deep in the mountains of the North's sparsely populated north east were supposed to build confidence ahead of the summit.
However, the closing of the site is not an irreversible move and would need to be followed by many more significant measures to meet the demand for real denuclearisation.
The president had agreed to the historic sit-down in March after months of trading insults and nuclear threats with the North Korean leader.
But after criticism from North Korea, Mr Trump cast doubt this week on whether the meeting would happen.
White House officials have privately predicted for weeks that the summit could be cancelled once or twice before actually taking place, owing to the hard-nosed style of the two leaders.
Mr Trump has seemed to welcome chatter of a Nobel Peace Prize, but that has yielded in recent weeks to the sobering prospect of ensuring a successful outcome with Mr Kim.