WASHINGTON (Reuters) - President-elect Joe Biden's incoming secretary of state, Antony Blinken, is set to pledge on Tuesday that he will work to revitalize damaged American diplomacy and build a united front to counter the challenges posed by Russia, China and Iran.

In a speech a day before Democrat Biden takes over from Republican Donald Trump, whose four-year tenure was marked by unilateral American action that often upset allies, Blinken will pledge to act together with them and with humility.