(CNN) President Donald Trump on Saturday said he wanted to see the elimination of trade barriers between the United States and its closest allies amid tensions over the Trump administration's move to impose steep tariffs on steel and aluminum imports from the EU, Canada and Mexico.

Speaking during an impromptu news conference at the G7 summit in Canada on Saturday, Trump said his ultimate goal was the elimination of all trade duties.

"Ultimately that's what you want," he said. "You want a tariff free. You want no barriers. And you want no subsidies. Because you have some cases where countries are subsidizing industries and that's not fair."

Later Saturday, Canadian Prime Minister Justin Trudeau said he would with "absolute certainty" impose retaliatory measures on July 1 to answer Trump's tariffs on steel and aluminum. He said the argument that Trump's tariffs on steel and aluminum are a matter of national security are "kind of insulting." Trudeau said Canadians are nice but added, "We will not be pushed around."

"I will always protect Canadian workers and Canadian interests," Trudeau said.

The remarks prompted Trump to accuse Trudeau of making "false statements" and to say the United States would not endorse the G7 communique.

"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!," the President tweeted on Saturday.

In a second tweet, Trump wrote, "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.' Very dishonest & weak. Our Tariffs are in response to his of 270% on dairy!"

Trump had warned hours earlier that the United States would not allow the continued imposition of trade barriers by other nations.

"Great meetings and relationships with the six Country Leaders especially since they know I cannot allow them to apply large Tariffs and strong barriers to ... U.S.A. Trade," Trump wrote in a pair of tweets. "They fully understand where I am coming from. After many decades, fair and reciprocal Trade will happen!"

"The United States will not allow other countries to impose massive Tariffs and Trade Barriers on its farmers, workers and companies," Trump continued. "While sending their product into our country tax free. We have put up with Trade Abuse for many decades — and that is long enough."

Allied responses

Trump's call for the elimination of trade barriers come amid fears of an all-out trade war after the US moved ahead with a 25% import tax on steel and a 10% on aluminum on most countries. The United States' closest trading partners -- the EU, Canada and Mexico -- have vowed to impose retaliatory tariffs on scores of US products beginning in the coming weeks.

Echoing Trudeau, British Prime Minister Theresa May said Saturday that the European Union also will impose countermeasures to the US tariffs.

"The EU -- of course, we operate as a member of the EU, as we currently are -- the European Union will impose countermeasures to the United States," May said. She added that the United Kingdom is a champion of free trade and would work to put in place free trade agreements with the United States and other countries once it leaves the European Union.

"We want to continue a good trading relationship with the EU, but we also want to take advantage once we are outside it of being able to negotiate our own agreements with other countries around the world because I think that is to the benefit of the people living in the United Kingdom" May said.

May characterized her relationship with Trump as "very good."

"We have a very good relationship with President Trump," May said. "We work with President Trump. The United Kingdom has a very good relationship with the United States."

G7 leaders had intended to use the summit to confront Trump on the tariffs, which they have described as protectionist and a threat to the global economy.

Trump said he discussed the idea of eliminating tariffs with his G7 counterparts.

"I did suggest it ... I guess they are going to go back to the drawing board and check it out," Trump said. "The relationships are very good," he added, mentioning his discussions with French and Canadian leaders specifically.

On Friday, French President Emmanuel Macron appeared to indicate room for negotiation ahead of a delayed meeting with Trump, telling reporters "Sometimes we disagree."

Globally, tariffs are close to their lowest levels ever — averaging around 2.9% — according to the latest data from the World Bank. Tariffs have been falling for decades due to free trade agreements.

Before departing the summit, Trump doubled-down on his assertions that the US has been subjected to unfair trade duties for many years. "It's going to change. Tariffs will come way down. We're like the piggy bank that everybody is robbing and that ends."

He added, "if they retaliate, they're making a mistake. We have a tremendous trade imbalance. When we try to bring our piece up a little bit so it's not so bad."

Pushback in Congress

Republican Sen. Ben Sasse of Nebraska said Trump's comments on eliminating tariffs among G7 nations would be "tremendous news" if the President is serious about the issue, adding, "I would happily carry his bag to every single meeting of those negotiations."

But Sasse said Trump's complaints that other countries have taken advantage of the United States are unfounded, adding that he recommended "less whining on the global stage."

"The simple fact is that more trade has been overwhelmingly beneficial to U.S. families and to net U.S. job creation for 75 straight years, and pretending America has been taken advantage of -- that is, pretending that we're losers -- isn't true.

"The constant victim-talk doesn't help anyone," he continued. "It doesn't help trade negotiations. And it doesn't help U.S. citizens understand the disruption in our economy that is actually coming from more technology and more automation, not from free trade agreements -- which have overwhelmingly benefited American families."

Earlier this week, Tennessee Sen. Bob Corker, who chairs the Senate Foreign Relations Committee, vowed to press ahead with legislation that would require lawmakers to approve of trade actions by the President that are done on the grounds of national security, despite opposition from Trump.

The President's characterization of the United States' relationships with allies as "a 10" when asked at the news conference about any tensions between his administration and other G7 nations also drew criticism from a senior European diplomat.

"He must mean there are 10 things on which we totally disagree," the diplomat said. "Or like the title of the movie '10 Things I Hate About You.'"

Trump has long criticized the United States' goods deficit. Economists point out that the current US economy is much more driven by services like hospitals, universities, tech companies and banks. Manufacturing, an industry Trump focuses on, makes up about 10% of US economic output.

Recent World Trade Organization data shows that America's average tariff for imported goods is 2.4%. Canada's average tariff for imported goods is 3.1%, and the EU's average tariff for imported goods is 3%.