U.S. President Donald Trump's planned 25% tariffs on all steel and aluminum imports would be added onto other levies on Canadian goods, resulting in a total 50% tariff, a White House official said on Tuesday.

At the moment, the U.S. is threatening two actions: a worldwide tariff of 25 per cent on steel and aluminum starting March 12, and it has also paused, until March 4, the threat of an economy-wide 25 per cent tariff on Canada and Mexico while it works on border-security deals with both countries.