Some countries could have special deals allowing them to avoid Donald Trump's proposed metal tariffs, officials have said.
A White House spokesperson has said that Canada, Mexico and others could see "carve-outs" initially.
But Trump adviser Peter Navarro warned that the continuation of the exemption would depend on renegotiating the North American Free Trade Agreement (Nafta) to the US's satisfaction.
Trump has said that steel products coming into the US will be subject to a 25 per cent tariff, while aluminium will carry a 10 per cent levy.
Yesterday the European Union outlined possible retaliation, which could see US peanut butter and bourbon become subject to steeper tariffs.
Meanwhile Trump's chief economic adviser Gary Cohn, a free trade supporter, stood down amid a disagreement over the policy.
But the Trump administration has indicated that it intends to go ahead. Press secretary Sarah Sanders said the measures will be signed by the end of the week.
Despite the threat of an impending trade war, Asian shares performed better overnight as the concessions for Canada and Mexico suggested that the policy would not be as severe as feared.