WASHINGTON (AFP) - US President Donald Trump dubbed a Democratic rival "Pocahontas" on Monday (Nov 27), during an event designed to honour Native American veterans in the White House's Oval Office.

Welcoming three aging Navajo "code talkers," who helped keep allied operations secret during World War II, Trump threw etiquette out the window to attack Senator Elizabeth Warren.

"You were here long before any of us were here," Trump said to one of the group.

"Although we have a representative in Congress who they say was here a long time ago. They call her Pocahontas," he continued, prompting staff to smother giggles.

It is a sobriquet Trump has repeatedly used to describe Warren, who has spoken about her mother's Native American ancestry and has been a political thorn in Trump's side.

During the remarks, Trump and the three veterans stood beneath a portrait of controversial president Andrew Jackson - who ordered the forced removal of Native Americans from their ancestral land, causing thousands to die.

The White House denied that Trump's remarks were a racial slur and claimed that what was "very offensive" was Warren "lying" about her ancestry.

Conservatives have accused Warren of exaggerating her Native American heritage in order to advance her career.