Canadian Prime Minister Mark Carney says US President Donald Trump "respected Canada's sovereignty" in the first call between the pair, who spoke amid an ongoing trade war between the two neighbours.

Trump has repeatedly suggested that Canada should become the 51st US state - an idea that has sparked widespread backlash among Canadians.

Carney, currently in the midst of an election campaign, described the call as "very constructive", while Trump said the call was "extremely productive".

Trump's planned 25% tariff on vehicle imports is due to come into effect on 2 April, which could prove devastating for the Canadian car industry.

Historically, Canadian leaders prioritise an early call with their US counterpart soon after becoming prime minister.

The call between Carney and Trump, however, is the first since the new prime minister took office on 14 March.

The Canadian prime minister's office said the two leaders agreed to begin comprehensive negotiations about a new economic and security relationship immediately following the election, which will be held on 28 April.

The US president's tone on Friday stood in contrast to his past remarks about Canada, particularly his frequent jabs at Carney's predecessor, Justin Trudeau, whom he mockingly referred to as "Governor Trudeau".

"I've always loved Canada," Trump told reporters after the call. "We had a very good conversation. The prime minister - they've got an election going on, so we're going to meet after the election."

The US has already partially imposed a blanket 25% tariff on Canadian goods, along with a 25% duty on all aluminium and steel imports. Canada has so far retaliated with about C$60bn ($42bn; £32bn) of tariffs on US goods.

The new car tariffs will come into effect next month, the White House has said. Taxes on parts are set to start in May or later.

On Thursday evening, Carney had said the US was "no longer a reliable trading partner" and that Canada's old relationship with the US "is over".

Carney, who leads Canada's Liberal Party, has vowed to impose retaliatory tariffs with "maximum impact" on the US.

On Friday, he conveyed the message once again to Trump, according to the statement from his office, suggesting further retaliatory tariffs could be announced if Trump moves ahead with threatened levies on 2 April.

The US president's proposed vehicle tariffs could impact as many as 500,000 jobs in the Canadian auto industry.

"I think things will work out very well between Canada and the United States," Trump said to reporters after the call.

"We have liberation day, as you know, on April 2, and I'm not referring to Canada, but many countries have taken advantage of us."

Worsening US-Canadian relations have become a key issue in Canada's general election.

After the call, Pierre Poilievre, leader of the Conservatives, the main opposition party, when asked about the apparent change in tone from Trump, said he "hopes" that was the case, adding: "We want to put an end to this crazy tariff chaos."

He also lambasted the Liberals, who have been in power since 2015, saying: "It's clear the president would like to keep the Liberals in power - they've been very good for his agenda. He wants to take our money and our jobs and Liberals have helped him do it."

On the campaign trail on Friday, Bloc Québécois leader Yves-François Blanchet, whose party represents Quebec's interests in Ottawa, expressed concern that Carney's statement about a forthcoming comprehensive discussion with Trump could mean the Liberal leader was open to conceding to US pressure.

Left-wing NDP leader Jagmeet Singh has previously referred to the tariffs as a "betrayal".

Trump has also warned Canada against working with the European Union to counter US reciprocal tariffs that he is expected to announce soon.

Any effort to do so, he said, would be met with "large-scale tariffs, far larger than currently planned".