U.S. tariffs on Canada, Mexico and China will go into effect on Saturday, White House spokeswoman Karoline Leavitt said Friday. 

The U.S. will impose 25% tariffs on Canada and Mexico, along with 10% on China, Leavitt said. She declined to say whether there will be exemptions.

Earlier, Reuters reported President Donald Trump was expected to announce new tariffs against Canada and Mexico to begin on March 1, but would include a process for the countries to seek specific exemptions for certain imports, three people familiar with the planning told Reuters.

Leavitt declared the Reuters March 1 report "false."

Reuters sources, who asked not to be named because they are not authorized to speak publicly on the matter, had said they did not have details on a final tariff rate, but noted Trump has consistently said that he plans to impose a 25% tariff on imports from the two countries on Saturday.

Separately, an administration official said Trump on Friday was reviewing tariff plans, which may allow for some exemptions. Still, any exemptions would be "few and far between," the official said.

While the announcement of tariffs may roil financial markets and strain the U.S. relationship with its top two trading partners, offering a 28-day window before implementation and a process for exemptions would suggest a more careful approach by the Trump administration.

It also would buy time for negotiations over actions by Canada and Mexico to meet Trump's stated goals for the duties, to pressure the two U.S. neighbors to halt the flow of illegal immigrants and deadly fentanyl across the U.S. border.