U.S. President Donald Trump said he will double the tariffs on steel and aluminum imports to 50 per cent next Wednesday. 

Trump initially announced the boosted duties on steel during a rally at U.S. Steel's Mon Valley Works–Irvin Plant near Pittsburgh Friday evening. He told a cheering crowd of steelworkers that the increased levies will "further secure the steel industry in the United States."

"Nobody is going to get around that," Trump said. 

In a post on social media after the rally, Trump said he would also be increasing tariffs on aluminum to 50 per cent. 

"Our steel and aluminum industries are coming back like never before," he wrote. "This will be yet another BIG jolt of great news for our wonderful steel and aluminum workers. MAKE AMERICA GREAT AGAIN!"

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The U.S. first imposed 25 per cent tariffs on steel and aluminum from Canada in March. As the duties have increased with Trump's tariffs, the government's producer price index found the price of steel products has increased roughly 16 per cent.

As of March, steel cost $984 US per metric ton in the United States, significantly more than the price in Europe ($690 US) or China ($392 US), according to the U.S. Commerce Department. The United States produced about three times more steel than it imported last year, with Canada, Brazil, Mexico and South Korea being the largest sources of steel imports.

The prime minister's office did not immediately comment.