Updated

President Trump fired off a series of tweets early Monday criticizing Canada and its prime minister over trade policy, saying that "Fair Trade is now to be called Fool Trade if it is not Reciprocal."

"According to a Canada release, they make almost 100 Billion Dollars in Trade with U.S. (guess they were bragging and got caught!). Minimum is 17B. Tax Dairy from us at 270%. Then [Canadian Prime Minister] Justin [Trudeau] acts hurt when called out!" Trump added.

He continued, "Sorry, we cannot let our friends, or enemies, take advantage of us on Trade anymore. We must put the American worker first!"

The president sent the messages from Singapore approximately 24 hours before his scheduled summit meeting with North Korean leader Kim Jong Un. Trump arrived in Singapore directly from a contentions G7 summit in Quebec, where he roiled his allies by first agreeing to a group statement on trade only to withdraw from it while complaining that he had been blindsided by Trudeau's criticism of Trump's tariff threats at a summit-ending news conference.

The attack on a longtime ally and its leader drew sharp criticism. German Chancellor Angela Merkel, who also attended the summit, told German public television that she found Trump's tweet disavowing the G7 statement "sobering" and "a little depressing."Merkel also said the European Union would "act" against the U.S. trade measures.

Undeterred, Trump continued to tweet Monday: "Why should I, as President of the United States, allow countries to continue to make Massive Trade Surpluses, as they have for decades, while our Farmers, Workers & Taxpayers have such a big and unfair price to pay? Not fair to the PEOPLE of America! $800 Billion Trade Deficit...And add to that the fact that the U.S. pays close to the entire cost of NATO-protecting many of these same countries that rip us off on Trade (they pay only a fraction of the cost-and laugh!). The European Union had a $151 Billion Surplus-should pay much more for Military!"

Then, Trump turned his sights on Merkel's government: ....Germany pays 1% (slowly) of GDP towards NATO, while we pay 4% of a MUCH larger GDP. Does anybody believe that makes sense? We protect Europe (which is good) at great financial loss, and then get unfairly clobbered on Trade. Change is coming!"

Earlier, the White House escalated the initial tirade and leveled more withering and unprecedented criticism against Trudeau, branding him a backstabber unworthy of Trump's time.

"There's a special place in hell for any foreign leader that engages in bad faith diplomacy with President Donald J. Trump and then tries to stab him in the back on the way out the door," Trump trade adviser Peter Navarro told "Fox News Sunday."

Canada's foreign minister, Chrystia Freeland, said her country "does not conduct its diplomacy through ad hominem attacks."

Trudeau, who had said at the news conference that Canada would retaliate for new U.S. tariffs, didn't respond to questions about Trump when the prime minister arrived at a Quebec City hotel Sunday for meetings with other world leaders. Freeland later told reporters that "we don't think that's a useful or productive way to do business."

A Trudeau spokesman, Cameron Ahmad, said Saturday night that Trudeau "said nothing he hasn't said before -- both in public and in private conversations" with Trump.

And, Roland Paris, a former foreign policy adviser to Trudeau, jabbed at Trump on Twitter: "Big tough guy once he's back on his airplane. Can't do it in person. ... He's a pathetic little man-child."

Trudeau said he had reiterated to Trump, who left the G7 meeting before it ended, that tariffs would harm industries and workers on both sides of the U.S.-Canada border. Trudeau told reporters that imposing retaliatory measures "is not something I relish doing" but that he wouldn't hesitate to do so because "I will always protect Canadian workers and Canadian interests."

Navarro said his harsh assessment of what "bad faith" Trudeau did with "that stunt press conference" on Saturday "comes right from Air Force One."

He said Trump "did the courtesy to Justin Trudeau to travel up to Quebec for that summit. He had other things, bigger things, on his plate in Singapore ... He did him a favor and he was even willing to sign that socialist communique. And what did Trudeau do as soon as the plane took off from Canadian airspace? Trudeau stuck our president in the back. That will not stand."

But the criticism left former Canadian prime minister Stephen Harper stumped. "I don't understand the obsession with trade relations with Canada," he told Fox Business Network's "Sunday Morning Futures." "We're the closest partners in the world and you don't want to see a dispute over one particular issue poison everything."

Trudeau had said Saturday that Canadians "are polite, we're reasonable, but also we will not be pushed around." He described all seven leaders coming together to sign the joint declaration despite having "some strong, firm conversations on trade, and specifically on American tariffs."