WASHINGTON — The a White House official said Wednesday that Mexico, Canada and other countries may be spared from President Donald Trump’s planned steel and aluminum tariffs under national security “carve-outs,” a move that could soften the blow amid threats of retaliation by trading partners and dire economic warnings from lawmakers and business groups.

Press secretary Sarah Huckabee Sanders told reporters the exemptions would be made on a “case by case” and “country by country” basis, a reversal from the policy articulated by the White House just days ago that there would be no exemptions.

The announcement came as congressional Republicans and business groups braced for the impact of expected tariffs of 25 percent on imported steel and 10 percent on aluminum, appearing resigned to additional protectionist trade actions as Trump signaled upcoming economic battles with China.

The looming departure of White House economic adviser Gary Cohn, a former Goldman Sachs executive who has opposed the promised tariffs, set off anxiety among business leaders and investors worried about a trade war.

“We urge you to reconsider the idea of broad tariffs to avoid unintended negative consequences to the U.S. economy and its workers,” 107 House Republicans wrote in a letter to Trump.

The a White House official said Trump was expected to make a final announcement as early as Thursday and officials were working to include language in the tariffs that would give Trump the flexibility to approve exemptions for certain countries.

“He’s already indicated a degree of flexibility, I think a very sensible, very balanced degree of flexibility,” Commerce Secretary Wilbur Ross told CNBC. “We’re not trying to blow up the world.”

Trump signaled other trade actions could be in the works. In a tweet, he said the “U.S. is acting swiftly on Intellectual Property theft.” A White House official said Trump was referencing an ongoing investigation of China in which the U.S. trade representative is studying whether Chinese intellectual property rules are “unreasonable or discriminatory” to American business.

Business leaders, meanwhile, continued to sound the alarm about the potential economic fallout from tariffs, with the president and CEO of the U.S. Chamber of Commerce raising the specter of a global trade war. That scenario, Tom Donohue said, would endanger the economic momentum from the GOP tax cuts and Trump’s rollback of regulations.