A furious President Trump on Saturday refused to sign a closing statement with the other Group of Seven countries, blaming the “very dishonest and weak” Canadian Prime Minister Justin Trudeau for the apparent change of heart.

“Based on Justin’s false statements at his news conference, and the fact that Canada is charging massive Tariffs . . . I have instructed our U.S. Reps not to endorse the Communique,” Trump tweeted as he flew away on Air Force One, en route to Singapore for Tuesday’s scheduled North Korea summit

The move capped a tense, two-day conference in which Trump used some hardball negotiating tactics on America’s top allies.

The tweets came as a shock ­after Trump gave a press conference striking a relatively conciliatory tone and Trudeau stated the US would sign the communique.

But the Canadian PM’s post-summit bluster — and threat of retaliatory tariffs on the US — ­appeared to set Trump off.

“PM Justin Trudeau of Canada acted so meek and mild during our @G7 meetings only to give a news conference after I left saying that, ‘US Tariffs were kind of insulting’ and he ‘will not be pushed around,’ ” Trump tweeted. “Very dishonest & weak.”

During his preflight press conference, Trump threatened to cut allies off from the massive US market if they don’t lower their trade barriers. “The gig is up.” he declared.

At the same time, Trump sought to entice foreign leaders with the prospect of turning the group into its own free-trade zone.

“That’s the way it should be — no tariffs, no barriers,” he said at a press conference in Charlevoix, Quebec, during the annual gathering of the world’s largest industrial democracies.

Trump’s free-trade remarks came just days after he imposed steep tariffs on steel and aluminum imports that infuriated America’s biggest trading partners.

At the same time, he tightened the screws on Britain, Canada, France, Germany, Italy and Japan, all of which apply tariffs, quotas and other barriers to incoming US goods.

“It’s going to stop, or we’ll stop trading with them,” Trump said.

He described his closed-door meetings with the six other leaders as “not contentious.”

“What was strong was the language that this cannot go on,” he said, referring to his insistence that the US is being victimized by trade deficits that hurt American workers.

“We’re the piggy bank that everybody is robbing. And that ends,” Trump asserted.

He continued to push his idea that Russia should be readmitted to the trade group. It lost its seat at the table in 2014 as punishment for President Vladimir Putin’s annexation of Crimea from Ukraine.

“I think the G-8 would be better. I think having Russia back in would be a positive thing,” he said. “We’re looking for peace in the world. We’re not looking to play games.”

The idea was greeted with disdain by his fellow leaders — all but Giuseppe Conte, Italy’s new prime minister.

“Russia should return to the G-8,” he tweeted Friday. “It is in everyone’s interest.”

Signaling the birth of a new international bromance, Trump called Conte “a really great guy” in a Saturday tweet.

“He will be honored in Washington, at the White House, shortly,” read the tweet. He will do a great job — the people of ­Italy got it right!”

Despite the obvious tensions, Trump spoke in glowing terms of his personal relationships with G-7 heads of state.

“I would say that the level of relationship is a 10,” he boasted. “We have a great relationship. Angela [Merkel] and Emmanuel [Macron] and Justin” — referring to the leaders of Germany, France and Canada by their first names.

“That doesn’t mean I agree with what they’re doing. And they know very well that I don’t,” he said.

French President Macron was more tactful: “It is obvious that we will have in the coming weeks, the next months, to continue to work,” he said.

Trudeau’s tough talk came hours after Trump’s departure.

“I highlighted directly to the president that Canadians did not take it lightly that the United States has moved forward with significant tariffs on our steel and aluminum industry,” he said.

Trudeau said his country will answer the US tariffs with levies of its own on July 1 unless Trump changes his mind.

German Chancellor Angela Merkel seconded Trump’s broad call for a reduction of tariffs and other trade barriers among G-7 members. “The pitfalls lie in the details,” she said.

In the face of a looming trade war, Trump issued a not-so-veiled threat.

“If they retaliate, they’re making a mistake,” he said. “We win that war a thousand times out of a thousand.” “They do so much more business with us than we do with them that we can’t lose… We win that war a thousand times out of a thousand.”