The founder of French extreme-right National Front party Jean-Marie Le Pen, who was kicked out of the party for xenophobic and anti-Semitic comments, has given his backing to US Republican presidential hopeful Donald Trump.

"If I was American I would vote for Donald Trump... may God protect him," Le Pen, 87, tweeted.

Le Pen was booted out of the National Front after a bitter feud with his daughter, Marine, who now leads the party, over his continued inflammatory, racist and xenophobic comments while she tries to polish her image to lure voters.

Last year he rehashed familiar comments about Nazi gas chambers being a "detail" of history for which he was found guilty of contesting crimes against humanity.

He has also in the past declared that the Nazi occupation was not “particularly inhumane” and that Ebola could clear up Europe's immigration problem "in three months".

On Friday, Trump disavowed the endorsement of another figure associated with inciting racial enmity, the former Ku Klux Klan grand wizard David Duke. The white nationalist told supporters: “He’s made it OK to talk about these incredible concerns of European Americans today.”

“Voting against Donald Trump at this point is really treason to your heritage,” Duke said.