(CNSNews.com) – President Trump’s decision to call off a planned summit with Kim Jong Un comes after heavy hints that China may have had something to do with the change in attitude and tone from Pyongyang, which recently resumed its customary U.S.-baiting rhetoric.

Trump in a letter to Kim cited “the tremendous anger and open hostility” expressed in a regime statement that insulted Vice President Mike Pence and warned of a “nuclear-to-nuclear showdown” as an alternative to talks with the U.S.

Speaking to reporters at a bill signing ceremony at the White House, Trump indicated that he had suspicions about what lay behind the shift in attitude by the regime.

He suggested that Kim been keen for the summit until something – he did not say what – occurred recently to change that.

“I think they want to do what’s right,” he said of the North Koreans. “I really think that they want to do – and it was only recently that this has been taking place. And I think I understand why it’s been taking place.”

Moments later he repeated the thought, saying that dialogue between the U.S. and North Korea “was good until recently, and I think I understand why that happened.”

Asked what he was referring to, Trump declined to say, joking that he would tell the reporter someday, and “you can write about it in a book.”

Earlier, however, Trump suggested that China, and possibly issues relating to trade, may be to blame.

In March – weeks after Trump first accepted his invitation for a summit – Kim paid his first visit abroad since becoming leader, traveling secretively to China for talks with President Xi Jinping.

Then early this month, days after a historic DMZ meeting with South Korean President Moon Jae-in, Kim paid an unexpected second trip to China, again meeting with Xi, in the port city of Dalian.

North Korea then began to raise doubts about the summit, and last Thursday Trump addressed the apparent hitch.

Speaking to reporters alongside NATO secretary-general Jens Stoltenberg, he said the meeting may yet go ahead and it may not – “we’ll see what happens.”

“I think things changed a little bit when they met with China,” he said. “As you know, Kim Jong-un had a second meeting with China, which was a little bit of a surprise meeting.”

“There has been a big difference since they had the second meeting with President Xi,” Trump said.

“I have a feeling, however, that for various reasons, maybe including trade, because they’ve never had this problem before – China has never had this problem with us – it could very well be that he’s influencing Kim Jong Un.”

Meeting with Moon at the White House earlier this week, Trump once again linked China to the souring, saying that “there was different attitude by the North Korean folks” after the second Kim-Xi meeting.

Although he said he was “not blaming anybody” and replied “no” when asked whether he thought China had discouraged Kim from going ahead with the summit, Trump also described Xi as “a world-class poker player.”

“I think things changed after that meeting,” he said. “So I can’t say that I’m happy about it.”

China is North Korea’s closest ally and has long accounted for the vast majority of its foreign trade. Late last year Beijing began reducing its imports from North Korea, in line with U.N. sanctions resolutions in response Pyongyang’s ballistic missile threats.

The stated reasons for North Korea’s dissatisfaction with the U.S. over recent weeks have been U.S. criticism of its human rights record; ongoing U.S.-South Korean joint military exercises, even though Kim apparently led the South Koreans to believe earlier that he understood those would continue; and suggestions by U.S. officials – disavowed by Trump himself – that North Korean denuclearization follow the “Libya model.”

A White House official briefing on background later Thursday said North Koreans had committed, during Secretary of State Mike Pompeo’s visit to Pyongyang this month, to hold a summit planning meeting in Singapore last week.

But though a U.S. delegation traveled to Singapore for the scheduled meeting the North Koreans never showed up, the official said.

Moon was meeting with his top security officials Friday to discuss the summit cancelation, and was quoted by Seoul’s Yonhap news agency as appealing to Trump and Kim to talk directly in a bid to salvage the initiative.

“Denuclearization of the Korean peninsula and the establishment of permanent peace are historic tasks that can neither be abandoned nor delayed,” the South Korean leader was quoted as saying.