The U.S. will set tariffs of 25 percent for steel and 10 percent for aluminum, the president said. It will apply the tariffs broadly, without targeting specific countries, and not impose quotas.

"People have no idea how badly our country has been treated by other countries. By people representing us who didn't have a clue," Trump said, arguing that trade trends "destroyed" American steel and aluminum industries.

Trump made the announcement as steel and aluminum executives, who back the tariffs, met with administration officials at the White House on Thursday. Confusion surrounded Trump's announcement as the administration struggled to agree on how to proceed.

"It's a mess," a White House aide told CNBC earlier in the day about the process.