An extension of these exemptions would be tied to progress in talks on the renegotiation of the North American Free Trade Agreement (NAFTA), the Washington Post said.
The announcement is expected Thursday, according to the report. White House spokesperson Sarah Sanders said earlier the details would be made known by the end of this week.
Last Thursday, US President Donald Trump said he would impose a 25-percent tariff on US imports of steel and a 10-percent tariff on aluminium for an indefinite period of time, despite criticism from US lawmakers and foreign leaders.
Earlier, US Treasury Secretary Steven Mnuchin said that the Trump administration was planning to impose new steel and aluminium tariffs "very, very quickly".