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U.S. President Donald Trump again attacked Canada’s dairy industry Thursday while calling the North American Free Trade Agreement (NAFTA) a “disaster for our country.”

Trump’s comments regarding Canada came shortly after he launched an investigation into whether foreign steel arriving in the U.S. threatens national security.

The president then broke from a prepared statement to attack Canada’s dairy, energy and lumber industries.

READ MORE: Why did Donald Trump attack the Canadian dairy industry?

“I wasn’t going to do this, but I was in Wisconsin the other day…Canada, what they’ve done to our dairy farm workers is a disgrace, it’s a disgrace,” Trump told reporters in the Oval Office. “I spent time with some of the farmers in Wisconsin and as you know rules, regulations, different things have changed and our farmers in Wisconsin and in New York State are being put out of business, our dairy farmers.”

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WATCH: Jackson Proskow reports on what’s behind the U.S. president’s surprisingly harsh language.

2:18 Trump slams Canada on trade again Trump slams Canada on trade again

Trump went on to suggest similar things are happening along the “northern border states with Canada, having to do with lumber and timber.”

“The fact is NAFTA, whether it’s Mexico or Canada, is a disaster for our country,” Trump said. “It’s a disaster. It’s a trading disaster.”

Trump’s latest comments were more extensive than his complaints earlier this week in Wisconsin about Canadian dairy regulations.

WATCH: Justin Trudeau responds to Trump’s attack on Canada’s dairy industry

3:08 Justin Trudeau responds to Trump’s attack on Canada’s dairy industry Justin Trudeau responds to Trump’s attack on Canada’s dairy industry

It’s a sign that Trump might be pushing for more extensive changes in the trading relationship with Canada than he has signalled previously, when he spoke merely of tweaking it.

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Trump says he’ll have more to say about upcoming NAFTA negotiations within a couple of weeks.

Trump initially launched the attack on the dairy industry Tuesday in an attempt to push his America First agenda by unveiling his “Buy American-Hire American” executive order.

READ MORE: Donald Trump takes aim at Canada’s dairy industry

“What’s happened to you is very unfair,” Trump said Tuesday. “It’s another very typical one-sided deal against the United States and its not going to be happening for very long.”

“Dairy trade between Canada and the U.S. massively favours the U.S., by a ratio of five to one,” said a statement released Thursday by foreign affairs minister Chrystia Freeland. “Canada is the second-largest export market for U.S. dairy products, surpassed only by Mexico.” Tweet This

“With respect to softwood lumber, our producers and workers have never been found in the wrong. The softwood industry supports thousands of jobs in both countries and has downstream benefits in communities across the continent.”

“Nothing is more essential to the U.S. economy than access to a secure and reliable source of energy. Canada is that source, providing the United States with 43 percent of its imported crude oil.”

The apparent growing trade dispute between the two countries stems from ultra-filtered milk, a product which allows for greater efficiency in cheese-making.

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American farmers were sending their ultra-filtered milk to Canada without being subject to tariffs, Ontario dairy farmers agreed last year to sell ultra-filtered milk to Canadian processors at prices competitive with international rates. Other provinces soon followed suit.

Most dairy products sent to Canada are subject to heavy tariffs.

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3:02 PM Trudeau discusses what he has learned about Trump since presidency PM Trudeau discusses what he has learned about Trump since presidency

However, ultra-filtered milk from the U.S. wasn’t subject to those tariffs because it came into use after NAFTA was approved in 1994.

Prime Minister Justin Trudeau spoke Thursday about Trump’s earlier attack on the dairy industry saying trade doesn’t always benefit everyone.

“As we approach trade, we have to make the arguments for it, we have to reassure people that we are being fair and responsible about trade and that there is ways to include everyone in the benefits of trade,” Trudeau said in an interview with Bloomberg news agency. “Whether it’s small, medium sized business, whether it’s agricultural producers. Any conversation around that starts with recognizing the facts.

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READ MORE: With new executive order, Trump could weaken NAFTA before he ‘tweaks’ it

“The U.S. has a $400 million dairy surplus with Canada, so it’s not Canada that is the challenge here and the way we approach our very constructive relationship with the United States on trade and on other thing is to base both around the facts of the issues and a shared desire to see citizens on both sides of our border succeed,” Trudeau said.

The prime minister noted that NAFTA creates millions of good jobs in both countries.

“We’re not going to overreact, we’re going to lay out the facts and we are going to have substantive conversations about how to improve the benefits for citizens on both sides of our borders,” Trudeau said.

–with a file from Global News reporter Kevin Nielsen and the Canadian Press