WASHINGTON (AP) — President Donald Trump declares he is "waiting" to see if North Korean leader Kim Jong Un will again "engage in constructive dialogue."

Trump opened the door for diplomacy Thursday just hours after he canceled a summit with Kim scheduled for next month in Singapore.

But he insisted that Kim reach out, placing the blame on the North Korean leader for the collapse of negotiations.

He also said that until that happened, tough sanctions on Pyongyang would continue and the U.S.-led "maximum pressure campaign is continuing."

Trump and Kim had been slated to meet June 12 for what White House officials had hoped would be a historic diplomatic breakthrough for the president.

They advised that the summit could be rescheduled.

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12:05 p.m.

President Donald Trump says the U.S. military is "ready if necessary" to respond to "foolish or reckless acts" by North Korea.

Trump also says he's been in touch with South Korea and Japan and that both allies are willing to bear much of the financial burden "if such an unfortunate situation is forced upon us."

Trump on Thursday announced he has called off a planned June 12 summit with North Korea's leader, Kim Jong Un, citing recent hostile statements by Kim's government.

North Korea overnight threatened nuclear confrontation with the U.S. and called Vice President Mike Pence a "political dummy."

Trump says hopefully "positive things" will take place with respect to North Korea's future. But he adds "If they don't we are more ready than we have ever been before."

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11:30 a.m.

Secretary of State Mike Pompeo says he was involved in discussions late Wednesday and early Thursday that led to President Donald Trump's decision to pull out of a planned summit with North Korean leader Kim Jong Un. But, he would not say exactly which, if any, other countries were given a head's up on the decision, including South Korea.

"I don't want to get into who all we notified," he told the Senate Foreign Relations Committee, adding: "The White House will speak to that at the appropriate time."

However, Pompeo, who met at the State Department on Wednesday with China's foreign minister, did say that he had not spoken to Chinese officials since the decision was made.

Asked about a report that South Korea had not been informed before the president's letter to Kim canceling the summit was made public, Pompeo maintained that Washington and Seoul were "in lockstep."

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11:20 a.m.

A prominent Russian lawmaker says the cancellation of the planned summit between President Donald Trump and North Korea's Kim Jong Un is a serious setback.

Konstantin Kosachev, chairman of the foreign affairs committee in the upper house of the Russian parliament, is quoted by the news agency Interfax as saying: "The rejection by Trump of conducting the American-North Korean summit undoubtedly is a serious blow to peaceful settlement in the region."

He adds that "it's already the second blow, after the exit from the agreement on the Iranian nuclear program, to global stability in general."

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11:15 a.m.

South Korean President Moon Jae-in's office says it is trying to figure out President Donald Trump's intentions in canceling a summit next month with North Korea's leader.

Moon played a prominent role in planning for the summit with Kim Jong Un, which was scheduled for June 12 in Singapore.

South Korea's Yonhap News Agency quoted a presidential office spokesman as saying they "are trying to figure out what President Trump's intention is and the exact meaning of it."

Trump released a letter to Kim on Thursday saying he had canceled the summit because of "tremendous anger and open hostility" expressed in a recent North Korean statement.

He did not elaborate, but a North Korean vice minister of foreign affairs issued a statement referring to comments by U.S. Vice President Mike Pence as "ignorant" and "stupid," and saying North Korea is just as ready to meet in a nuclear confrontation as at the negotiating table.

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11:05 a.m.

A Republican senator often critical of Donald Trump says the president "made the right call" in canceling a summit with North Korea's leader.

Sen. Ben Sasse of Nebraska says Kim Jong Un is a "murderous despot and habitual liar." Sasse is often critical of Trump but is siding with the president on his decision Thursday to pull out of the summit that had been planned for June 12 in Singapore.

Trump cited recent aggressive statements from Kim's government for his decision to cancel the meeting.

Sasse adds in a statement that if North Korea wants diplomacy, "it should know that half-measures and spin about its nuclear program won't cut it."

Sasse is a member of the Senate Armed Services Committee,

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10:55 a.m.

The U.N. chief says he is "deeply concerned" by the cancellation of the planned summit between U.S. President Donald Trump and North Korean Leader Kim Jong Un.

Antonio Guterres told an audience at the University of Geneva on Thursday that he was urging the parties to keep working "to find a path to the peaceful and verifiable denuclearization of the Korean Peninsula."

Guterres' comments came as he laid out his disarmament agenda, warning that nuclear agreements between states have been threatened like never before.

Trump announced Thursday that he was canceling the June 12 summit in Singapore with Kim following hostile comments. Overnight, Kim's government threatened nuclear confrontation and called Vice President Mike Pence a "political dummy."

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10:45 a.m.

House Speaker Paul Ryan says achieving a peaceful resolution to the nuclear standoff on the Korean Peninsula will require "a much greater degree of seriousness" from Kim Jong Un.

President Donald Trump announced Thursday that he has canceled a June 12 summit in Singapore with the North Korean leader, citing hostile comments from Kim. Overnight, Kim's government threatened nuclear confrontation and called Vice President Mike Pence a "political dummy."

Ryan says in a statement Thursday that Kim's government has long given ample reason to question its commitment to stability.

The Republican says that, until a peaceful resolution is achieved, Congress has provided "significant tools" to hold North Korea accountable.

Ryan says the U.S. must continue the "maximum pressure" campaign that Trump and others say brought North Korea to the table in the first place.

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10:35 a.m.

Secretary of State Mike Pompeo says North Korea did not respond to repeated requests from U.S. officials to discuss logistics for the now-canceled summit between President Donald Trump and North Korean leader Kim Jong Un.

Pompeo told the Senate Foreign Relations Committee on Thursday that the lack of response was an additional reason for Trump's decision to call off the meeting. Trump cited recent bellicose comments from the North in a letter to Kim released by the White House.

Pompeo says: "We had received no response to our inquiries from them."

Pompeo says the North's attitude changed markedly since he returned from a trip to Pyongyang earlier this month, when he met with Kim and secured the release of three American prisoners being held there.

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10:30 a.m.

A senior Democratic senator says President Donald Trump's withdrawal from a planned summit with North Korea shows the consequence of his failure to prepare properly.

Sen. Bob Menendez of New Jersey said Thursday that the withdrawal shows "the art of diplomacy is a lot harder than the art of the deal."

The top-ranking Democrat on the Senate Foreign Relations Committee says it's "pretty amazing" that Trump's Republican administration would be shocked that North Korea "is acting as North Korea might very well normally act."

He adds: "I'm not sure that constantly quoting the Libya model is the diplomatic way to try to get to the results that we seek in North Korea because that didn't work out too well for Gadhafi."

Menendez was speaking Thursday at a committee hearing attended by Secretary of State Mike Pompeo.

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10:05 a.m.

President Donald Trump says North Korea's leader should not "hesitate to call me or write" if he changes his mind about their now-canceled summit.

Trump announced Thursday that he had canceled a summit planned with Kim Jong Un in Singapore on June 12.

Trump released a letter to Kim saying his decision was based on "the tremendous anger and open hostility" in Kim's most recent statement. Trump did not explain what triggered his decision.

But in a statement, the North Korean government had referred to Vice President Mike Pence as a "political dummy" and said it is just as ready to meet in a nuclear confrontation as at the negotiating table.

But Trump tells Kim "please do not hesitate to call me or write" should he change his mind about a one-on-one meeting.

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10 a.m.

President Donald Trump is telling North Korea's Kim Jong Un in a letter that the world is losing a "great opportunity for lasting peace and great prosperity and wealth" now that their summit has been canceled.

Trump on Thursday canceled the planned June 12 summit in Singapore with Kim, citing the "tremendous anger and open hostility" in a recent statement from North Korea.

In the statement, the North Korean government referred to Vice President Mike Pence as a "political dummy" and said it is just as ready to meet in a nuclear confrontation as at the negotiating table.

Trump says in the letter: "This missed opportunity is a truly sad moment in history."

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9:50 a.m.

President Donald Trump is canceling the planned June 12 summit with North Korea's Kim Jong Un, citing the "tremendous anger and open hostility" in a recent statement from North Korea.

Trump says in a letter to Kim released Thursday by the White House that based on the statement, he felt it was "inappropriate, at this time, to have this long-planned meeting."

The president says the North Koreans talk about their nuclear capabilities, "but ours are so massive and powerful that I pray to God they will never have to be used."