The United States imposed the "Section 232" tariffs on steel and aluminum nearly a year ago to protect domestic producers on national security grounds.

Donald Trump's steel and aluminum tariffs contradict a key component of the new North American trade agreement dealing with cars.

Sources say Thursday's talks between Foreign Affairs Minister Chrystia Freeland and U.S. trade ambassador Robert Lighthizer were dominated by efforts to secure a commitment from the Americans that a new NAFTA deal would mitigate the risk of such tariffs.