US President Donald Trump has railed against the "cancel culture" of those who toppled monuments during recent anti-racism protests, in a speech to mark 4 July at Mount Rushmore.

He condemned those who targeted statues of Confederate leaders as "angry mobs".

Mr Trump accused protesters of "a merciless campaign to wipe out our history, defame our heroes, erase our values, and indoctrinate our children".

"We will not be silenced," he said.

Addressing Mount Rushmore itself, the president said the South Dakota landmark would "stand forever as an eternal tribute to our forefathers and to our freedom".

"This monument will never be desecrated, these heroes will never be defaced," he told a cheering crowd.

The president added that people who target "symbols of national heritage" will face "the fullest extent of the law". He said those who defaced statues could be sentenced to 10 years in jail, referring to a recent executive order he signed on protecting monuments.