Donald Trump has accused Elizabeth Warren of being a "racist" and a "fraud', after the Massachusetts senator appeared alongside his Democratic rival to call for Americans to unite against him.

The attack came as Mrs Warren, a liberal favourite, painted the presumptive Republican nominee as a selfish "money grubber" whilst at the same time helping give Mrs Clinton's campaign a populist hue.

The real estate mogul re-upped an old controversy over whether Mrs Warren has wrongly portrayed herself as being of American Indian descent: "She made up her heritage which I think is racist," he said in a phone interview, accusing the senator of using the claim "to advance her career".

Mr Trump once again referred to Mrs Warren as "Pocahontas", a nick name he developed for some weeks ago, that American Indian groups have denounced as offensive.