Mitt Romney: 'Donald Trump is a fraud'

One of the most senior figures in the US Republican party, Mitt Romney, has issued a scathing verbal attack on the frontrunner for the party's presidential nomination, Donald Trump.

In a speech in Utah, Mr Romney attacked Mr Trump as ''a phoney, a fraud''.

''His promises are as worthless as a degree from Trump University,'' he said.

Mr Trump has meanwhile mocked Mr Romney on Twitter as a "failed candidate" who should not advise on electability.