President Donald Trump on Thursday said his proposed tariffs on Mexico and Canada will go into effect March 4 and that China will be charged an additional 10% tariff on the same date.

The sweeping 25% tariffs on imports from Mexico and Canada had been paused on Feb. 3 for one month. But the Trump administration has recently sown confusion about whether they would go back into effect when the delays expired.

In a Truth Social post Thursday morning, Trump clarified that they would.

He said, without providing evidence, that illicit drugs "are still pouring into our Country from Mexico and Canada at very high and unacceptable levels," despite pledges from both U.S. neighbors to boost their efforts to police their borders.

"We cannot allow this scourge to continue to harm the USA, and therefore, until it stops, or is seriously limited, the proposed TARIFFS scheduled to go into effect on MARCH FOURTH will, indeed, go into effect, as scheduled," Trump wrote.

He also announced that China, which already faces 10% U.S. tariffs on its products, "will likewise be charged an additional 10% Tariff on that date."

Trump added in his post, "The April Second Reciprocal Tariff date will remain in full force and effect."

A White House official confirmed to CNBC later Thursday morning that the new duties on Beijing mean U.S. tariffs on Chinese imports will total 20%.

Dow Jones Industrial Average futures turned slightly negative following Trump's post, but rose when markets opened.

The president's post contradicted a timeline laid out about an hour earlier Thursday morning on CNBC's "Squawk Box" by White House National Economic Council Director Kevin Hassett.

Citing Trump's public remarks at his first Cabinet meeting Wednesday, Hassett said the president would decide on "tariff policy for all countries" after evaluating a study scheduled to come out April 1.

Trump in that meeting "extended by saying that we're going to deal with Mexico and Canada, presumably the same time we deal with everything else," Hassett said.

The president has made tariffs a core piece of his second-term agenda, touting them as a purported revenue source and wielding them as a threat against other countries.

In addition to the tariffs on China, Mexico and Canada, Trump has ordered global 25% tariffs on imports of steel and aluminum, which are set to take effect March 12.

On Feb. 13, Trump signed a presidential memorandum on his plan to impose reciprocal tariffs on foreign nations that have duties on U.S. imports. In addition to the tit-for-tat tariffs, Trump's plan would treat certain other policies, such as the use of value-added taxes, as unfair trade practices that warrant tariffs in response.

— CNBC's Megan Cassella and Eamon Javers contributed to this report.