President Donald Trump insists he is "not backing down" on his plan to impose stiff tariffs on imported steel and aluminium despite anxious warnings from House Speaker Paul Ryan and other congressional Republicans of a possible trade war.

President-elect Donald Trump appointed a controversial media figure to a key job as he began to shape his White House team.

With calls growing for him to quit, Bernie Sanders went to the White House for a meeting that President Barack Obama hoped to use to try to nudge the Vermont senator to accept defeat in the Democratic race.

An aide to House Speaker Paul Ryan says the Wisconsin Republican will formally rule running for president this year.