US President Donald Trump hit back at Canada on Sunday after Prime Minister Mark Carney announced retaliatory tariffs on the United States following a breakdown in trade negotiations.

“Canada wants the benefits of being a state, without being one!!!” Trump said in a post on Truth Social.

“They have also charged our great farmers, for many years, massive amounts of tariffs. No more!!!” he said.

Carney said on Saturday that new Canadian tariffs would take effect on September 8, notably targeting the US steel and dairy industries.

New 50 per cent US tariffs impacting about $20 billion worth of goods, or 5.5pc of Canadian exports to the US, came into force on Saturday.

Impacted products range from hockey sticks to cement.

“You’re at war when you get attacked. We got attacked,” Carney said a day earlier.

New Canadian tariffs will notably target the US steel and dairy industries and take effect on September 8. More details would come next week, Carney said.

Trump had previously said Washington “should be able to have a deal with Canada,” citing his “good relationship” with Carney.

But on Saturday, Canada’s prime minister said Trump set conditions that were ultimately unacceptable even though earlier talks had been positive.

“In recent days, the United States proposed new terms that were uneconomic, unfair and undermined the net benefits for Canada, and called into question the reliability of any deal,” Carney said in Ottawa.

“We cannot accept what they’ve offered, and we will not give what they’ve asked.”

US Trade Representative Jamieson Greer told the New York Times on Saturday that the US had offered to reduce its tariffs on steel, aluminium and autos, as well as eliminate a recently imposed tariff on Canadian lumber.

Greer said those measures would have given Canada “the most preferential treatment of any trading partner,” according to the Times.

Greer told Fox News on Saturday that Washington was “moving forward with measures that respond to Canadian retaliation.” He said no new talks were planned with Canadian negotiators.

A senior US official characterised this week’s talks in Washington as candid and not acrimonious.