US PRESIDENT Donald Trump signed an order imposing stiff tariffs on imports from Canada, Mexico and China at the weekend, triggering a trade war as the three countries swiftly retaliated.

The Republican president claimed on social media that the tariffs, which take effect tomorrow, were necessary “to protect Americans,” as he pressed all three nations to curb the manufacture and export of illicit drug fentanyl and for Canada and Mexico to reduce illegal migration into the US.

The tariffs, if sustained, could cause domestic inflation to significantly worsen, threatening to derail Mr Trump’s pledge of bringing down the cost of groceries, petrol, housing, cars and other goods. They also risk throwing the global economy into turmoil just two weeks into his second term.