President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE on Sunday warned other countries that the U.S. would retaliate if they placed trade barriers and tariffs on U.S. exports.

"The United States is insisting that all countries that have placed artificial Trade Barriers and Tariffs on goods going into their country, remove those Barriers & Tariffs or be met with more than Reciprocity by the U.S.A. Trade must be fair and no longer a one way street!" Trump said in a tweet.

The United States is insisting that all countries that have placed artificial Trade Barriers and Tariffs on goods going into their country, remove those Barriers & Tariffs or be met with more than Reciprocity by the U.S.A. Trade must be fair and no longer a one way street! — Donald J. Trump (@realDonaldTrump) June 24, 2018

Trump's tweet comes days after he threatened to impose a 20 percent tariff on all European cars entering the U.S.

The statement came after Commerce Secretary Wilbur Ross told U.S. lawmakers that the administration was starting an investigation to determine whether foreign autos and auto parts threaten national security.

Trump has escalated his rhetoric on trade toward other countries, including U.S. allies, in recent weeks, vowing to take care of farmers and manufacturers who have grown increasingly concerned about the tit-for-tat tariff battle between the U.S. and its allies.

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Trump also continued to escalate trade rhetoric with Canada last week, creating more uncertainty around the future of the North American Free Trade Agreement.

"They buy shoes and they wear them. They scuff them up to make them sound old, or look old," Trump said. "No, we're treated horribly."

In a speech at the Nevada state GOP convention on Saturday, Trump briefly mentioned Canadian Prime Minister Justin Trudeau, calling the country's tariffs on U.S. products "ridiculous."

Last week, Trump followed through on his promise to punish China for its trade practices, announcing he would impose tariffs on $50 billion worth of Chinese goods.

Trump raised alarm of looming trade war this week by asking his trade representative to evaluate another round of tariffs on $200 billion in Chinese products. The move came after China imposed its own retaliatory measure against the United States.