Rex Tillerson ducks question on whether he branded Trump 'a moron'

The strained relationship between President Donald Trump and US secretary of state Rex Tillerson came under renewed focus on today, as the nation's top diplomat insisted Mr Trump has not undermined him even as he again refused to deny calling the president "a moron".

Tensions between the two men have grown while the nation faces a series of high-stakes international crises, including the threat posed by North Korea and fate of the Iran nuclear deal, and threatens to sow doubt about American allies as to whether Mr Tillerson can speak authoritatively for the United States.