U.S. President Barack Obama urged Republican presidential nominee Donald Trump to "stop whining" about the Nov. 8 election being rigged, saying no serious person could suggest U.S. elections could be manipulated because of their decentralized nature.

"I have never seen in my lifetime, or in modern political history, any presidential candidate trying to discredit the elections and the election process before votes have even taken place. It's unprecedented," the Democratic president said.

"I'd invite Mr. Trump to stop whining, and go try to make his case to get votes," Obama said at a joint White House news conference with Italian Prime Minister Matteo Renzi.

Trump has recently ratcheted up his complaints that the election is "rigged" against him amid poll numbers suggesting he is likely to lose the election in November.

In a Friday speech, Obama praised Democratic nominee Hillary Clinton as someone who doesn't whine.

"No matter how tough the odds, no matter how much people try to knock her down, she doesn't point fingers or whine, she doesn't talk about how everything's rigged. She just works harder and gets the job done and never ever quits," Obama said at the time.



—CNBC's AJ Vielma contributed to this report.