Canada is considering retaliatory measures against the United States, a government source said Friday, as the country was urged to take seriously Donald Trump's threats to impose tariffs on Canadian imports.

A senior official, speaking on background, told AFP the government is preparing for all eventualities, including possible retaliatory tariffs. A list of US items to target was already being put together, the official added.

President-elect Trump announced the pending import tariffs against neighbors Canada and Mexico and also rival China in social media posts on Monday, demanding that the top three US economic partners stop illegal immigration and drug smuggling into the United States.

Some have suggested the threat may be bluster, or an opening salvo in future trade negotiations. But Canadian Prime Minister Justin Trudeau rejected those views.

"Donald Trump, when he makes statements like that, he plans on carrying them out," Trudeau told reporters in Prince Edward Island province. "There's no question about it." The Canadian leader spoke with Trump by telephone this week about trade and border security, describing it as a "good" conversation.

On Friday he said he has impressed upon Trump "the need to work together to ensure prosperity on both sides of the border."

He said it was important to further demonstrate that 25 percent tariffs on Canadian imports would harm not just Canadians, but Americans too.

"Ultimately, it is through lots of constructive conversations with President Trump that I'm going to have that will keep us moving forward on the right track for all Canadians," he said.

In 2023, more than three-quarters of Canadian exports, or Can$592.7 billion ($423 billion), went to the United States. Nearly two million Canadian jobs are dependent on trade.

Immediately following Trump's election, Deputy Prime Minister Chrystia Freeland reassembled a group of ministers to manage Canada-US relations, as was done during Trump's first stint in the White House.

They are tasked with preparing responses to US actions and lobbying US lawmakers and members of Trump's inner circle.

During Trump's first term, when he imposed tariffs in 2018 on Canadian steel and aluminum, Canada responded tit-for-tat.

However it chose to target US products for their political rather than economic impact, such as Florida orange juice and Kentucky bourbon -- both hailing from states led by Republicans.