US President Barack Obama urges Donald Trump to "stop whining" about the November 8 election being rigged.

US President Barack Obama has scolded Donald Trump over his repeated claims the upcoming election is "rigged" against him, telling the Republican presidential candidate to "stop whining".

At a joint news conference in the White House Rose Garden following meetings with Italian Prime Minister Matteo Renzi, Obama was asked about Trump's claims that US cities are rife with voter fraud and that there were efforts to "rig the election at the polling place."

"I'd invite Mr Trump to stop whining and go try to make his case to get votes," Obama advised.

CARLOS BARRIA Barack Obama: "I'd invite Mr Trump to stop whining and go try to make his case to get votes."

For many months, Trump has raised the possibility of illegal activities that could tarnish the November 8 election result, and he has urged his supporters to show up at polling locations on Election Day.

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KEVIN LAMARQUE Barack Obama made the comments during a joint White House press conference with Italian Prime Minister Matteo Renzi.

In recent days, Trump's rhetoric at campaign appearances and on social media about a rigged election has intensified as his standing in public opinion polls has fallen.

Referring to Trump's contention, Obama said: "It's unprecedented. It happens to be based on no facts."