US President Donald Trump said on Thursday that all trade talks with Canada were terminated following what he called a fraudulent advertisement in which former President Ronald Reagan spoke negatively about tariffs.

"Based on their egregious behavior, ALL TRADE NEGOTIATIONS WITH CANADA ARE HEREBY TERMINATED," Trump wrote on Truth Social.

The advertisement, which showed Reagan criticising tariffs on foreign goods and saying they caused job losses and trade wars, reportedly caught Trump's attention earlier this week.

Ontario Premier Doug Ford confirmed the US president had seen it.

"I heard that the president heard our ad. I'm sure he wasn’t too happy," Ford said on Tuesday.

In a separate post late Thursday, Trump reiterated that he was ending “all trade negotiations” with Canada because of recent television ads protesting US tariffs, calling them “egregious behaviour” aimed at influencing US court decisions.

Trump has used tariffs as leverage on many countries around the world. His trade war has raised US tariffs to their highest levels since the 1930s, and he has regularly threatened more duties, sparking concerns among businesses and economists.

Canadian Prime Minister Mark Carney told reporters on Thursday that Canada will not allow unfair US access to its markets if talks on various trade deals with Washington fail.

He also said he aims to double Canada’s exports to countries outside the US because of the threat posed by Trump’s tariffs.

Trump imposed tariffs on Canadian steel, aluminum and autos earlier this year, prompting Ottawa to respond in kind. The two sides have been in talks for weeks on a potential deal for the steel and aluminum sectors.

Next year, the US, Canada and Mexico are due to review their 2020 continental free-trade agreement.