Fears of a trade war are mounting after China threatened "a necessary response" to planned US tariffs on steel and aluminium imports.
President Trump is expected to approve the duties at a ceremony on Thursday, though officials have said that could slide into Friday due to legal reasons.
Faced with opposition from congressional Republicans, the White House has indicated some countries, notably Canada and Mexico, could be offered exemptions from the planned tariffs.
White House Press Secretary Sarah Huckabee Sanders said: "There are potential carve outs for Mexico and Canada based on national security and possibly other countries as well based on that process. (Questions off camera)..."Again that would be a case by case and country by country basis, but it would be determined whether or not there is a national security exemption."
On Monday, Trump said Canada and Mexico would only be excluded after the successful renegotiation of the North American Free Trade Agreement (NAFTA).
The US tariffs could see a 25 percent hike on steel, and 10 percent on aluminium to counter cheap imports.
Earlier, Beijing said it would not take such a move lying down.
Chinese Foreign Minister Wang Yi said: "History has taught us that trade wars are never the solution. In a globalised world, choosing a trade war is the wrong prescription. As a result, it will only hurt both sides, and China will surely make a justified and necessary response."
Europe has also warned president Trump to expect retaliatory strikes against iconic American products such as Levi's jeans, Harley-Davidson bikes and bourbon whiskey, among others.