TORONTO – Canada on Thursday hailed the news it would not immediately be subject to US tariffs on steel and aluminum while promising to continue lobbying Washington until the threat of duties had disappeared.

President Donald Trump announced the imposition of 25% tariffs on steel imports and 10% for aluminum on Thursday but said Canada and Mexico would be exempt as long as talks to update the NAFTA trade deal progressed.

"Today is a step forward. There's more hard work to do, and we will not let up," said Canadian Foreign Minister Chrystia Freeland, who led what officials called an aggressive lobbying campaign to persuade Trump to grant an exemption.

Freeland, speaking in Toronto, also told reporters that "this work continues and it will continue until the prospect of these duties is fully and permanently lifted".

Pressed repeatedly about Trump's decision to link the tariff exemption to progress at the talks on NAFTA, which are going slowly amid US demands for major changes, Freeland said Canada considered the two tracks to be totally separate.

Canada is the largest supplier of both steel and aluminum to the United States.

Freeland, who last week threatened retaliation if tariffs were to be imposed, said Canada would protect its steel and aluminium industries.

"We will not stand by while Canadians' livelihoods are put at risk," she said.

Prime Minister Justin Trudeau said earlier on Thursday there was a "level of confidence" that the country's close relationship with the United States would protect it from the US tariffs.

Trudeau told CBC radio he believed there would be "a recognition that Canada is in a particular situation in our close relationship" with the United States.

Trudeau spoke separately by phone on Thursday with US Senate Majority Leader Mitch McConnell and House of Representatives speaker Paul Ryan, prominent Republican critics of the tariffs proposal.

Trudeau called Trump on Monday to stress his concerns about the tariffs, officials said.

"We are continuing to push on getting the right deal for Canada, getting the right deal for Canadians, getting the right deal for everyone," Trudeau said in a separate interview on Breakfast Television.