QUEBEC CITY • President Donald Trump upended two days of global economic diplomacy, refusing to sign a joint statement with the United States' allies, threatening to escalate his trade war on the country's neighbours and deriding Canada's Prime Minister as "very dishonest and weak".

In a remarkable pair of acrimony-laced tweets from aboard Air Force One as he flew away from the Group of 7 summit towards a meeting with North Korea's leader, Mr Trump lashed out at Mr Justin Trudeau. He accused the Canadian Prime Minister, who hosted the seven-nation gathering, of making false statements.

Literally moments after Mr Trudeau's government proudly released the joint statement, noting that it had been agreed to by all seven countries, Mr Trump blew apart the veneer of cordiality that had prevailed throughout the two days of meetings in a resort town on the banks of the St Lawrence River.

"Based on Justin's false statements at his news conference, and the fact that Canada is charging massive Tariffs to our U.S. farmers, workers and companies, I have instructed our U.S. Reps not to endorse the Communique as we look at Tariffs on automobiles flooding the U.S. Market!" Mr Trump wrote.

A few hours earlier, Mr Trudeau said the seven nations had reached broad agreements on a range of economic and foreign policy goals. But he acknowledged that deep disagreements remained between Mr Trump and the leaders of the other nations, especially on trade.

Mr Trudeau had sought to play down personal clashes with Mr Trump as he wrapped up the summit, calling the meeting "very successful" and saying he was "inspired by the discussion". But he also pledged to retaliate against the US tariffs on steel and aluminium products in defence of Canadian workers.

Mr Trump, who apparently saw Mr Trudeau's news conference on television aboard Air Force One, was clearly enraged. "PM Justin Trudeau of Canada acted so meek and mild during our @g7 meetings," Mr Trump said in a second tweet, "only to give a news conference after I left saying that, 'US Tariffs were kind of insulting' and he 'will not be pushed around.' Very dishonest & weak. Our Tariffs are in response to his of 270% on dairy!"

Not long after, Mr John Bolton, the President's national security adviser, tweeted a dramatic photo of Mr Trump, arms crossed and scowling, looking defiant as the leaders of the other nations stood in a circle around him.

"Just another #G7 where other countries expect America will always be their bank," Mr Bolton wrote as Mr Trump's plane stopped for refuelling at Souda Bay on the Greek island of Crete. "The president made it clear today. No more."

Mr Trudeau's office responded to Mr Trump's Twitter barrage with a carefully worded statement.

"We are focused on everything we accomplished here at the summit," said Mr Cameron Ahmad, a spokesman for Mr Trudeau. "The prime minister said nothing he hasn't said before - both in public, and in private conversations with the president."

White House economic adviser Larry Kudlow kept up the pressure yesterday, telling CNN's State Of The Union talk show that Mr Trump had to pull out of a joint G-7 statement because the Canadian leader had "stabbed us in the back".

"He held a press conference and he said the US is insulting. He said that Canada has to stand up for itself. He says that we are the problem with tariffs. The non-factual part of this is - they have enormous tariffs," Mr Kudlow said. "He really kind of stabbed us in the back."

Mr Trump's outburst had been foreshadowed for days leading up to the Canada summit, with the US President and his G-7 counterparts trading sharp-edged barbs that included threats of punches and counter-punches on tariffs.

That was followed by 48 hours of tense and often confrontational closed-door discussions between Mr Trump and the leaders of the US' closest allies - France, Britain, Canada, Japan, Italy and Germany - in the hopes of resolving a brewing trade war among friends. Instead, the gathering apparently served to further inflame Mr Trump's belief that the US is being treated unfairly by countries with which prior presidents had long ago negotiated trade agreements for the flow of goods and services.

The result was a slow-rolling collapse of the fragile alliances at the summit.

Reporters on Air Force One had been told the US would sign the joint statement. And minutes after the President's tweets, reporters were sent an e-mail that had clearly been prepared earlier touting Mr Trump's participation in the summit, complete with photos.

Earlier in the day, before Mr Trump left the summit, he brought up the dramatic prospect of completely eliminating tariffs on goods and services, even as he threatened to end all trade with the US' partners if they did not stop what he said were unfair trade practices.

Mr Trump, speaking to reporters at the end of the contentious meeting, said that eliminating all trading barriers would be "the ultimate thing". He railed about what he called "ridiculous and unacceptable" tariffs on US goods and vowed to end them.

"It's going to stop or we'll stop trading with them. And that's a very profitable answer, if we have to do it, " he said, adding: "We're like the piggy bank that everybody's robbing - and that ends."

The other six leaders were defiant in the face of Mr Trump's threats. "I have made it very clear to the President that it is not something we relish doing, but it is something that we absolutely will do," Mr Trudeau said. "As Canadians, we are polite, we're reasonable, but also we will not be pushed around."

Mr Macron said the trade debates at the summit were "sometimes quite heated". Asked who won the tug-of-war with Mr Trump, Mr Macron said: "There is no winner, there are only losers when you take that strategy."

British Prime Minister Theresa May, meanwhile, blasted Mr Trump's tariffs. She said she had registered "our deep disappointment at the unjustified decision" and that the loss of trade through tariffs would "ultimately make everyone poorer".

Mr Trump's surprise proposal for a tariff-free G-7 followed from a conversation he had on Air Force One heading to Canada with Mr Kudlow.

Mr Kudlow, a self-described "lifelong free trader", had written an op-ed article in The Washington Post last Thursday saying he did not prefer tariffs but that Mr Trump's actions were "a wake-up call to the dangers of a broken trading system that is increasingly unfree".

Mr Trump and Mr Kudlow discussed the article on the plane, but the President surprised even his own team by raising the idea with the other leaders.

Asked late on Saturday what he told Mr Trump about the surprise proposal for a tariff-free zone, Mr Macron said, with a smile: "Be my guest, if that's your wish."

NYTIMES