US President Barack Obama criticized Republican presidential candidate Donald Trump for questioning the legitimacy of next month's presidential election.

Speaking at a campaign rally in Florida for Hillary Clinton, the Democratic Party nominee for president, Obama called Trump's comments "dangerous." He said Trump's efforts to "sow the seeds of doubt" about the election process undermined the democratic process and emboldened the country's enemies.

"When you try to sow the seeds of doubt in people's minds about the legitimacy of our election, that undermines our democracy," Obama told the crowd. "When you suggest rigging or fraud without a shred of evidence, when last night at the debate, Trump becomes the first major party nominee in American history to suggest that he will not concede despite losing...that is not a joking matter."

Obama urged the crowd at the rally to vote, vote early, and give Clinton a "big" win.

During the third and final presidential debate with Clinton Wednesday night, Trump refused to say whether he would follow tradition and concede the election if he loses the race for the White House on November 8.

The "rigged" election myth

For weeks, Trump has been pushing the idea that the system is rigged against him, while favoring Clinton, a former secretary of state, US senator and first lady.

On Thursday, Trump seemed to try and make light of the situation while campaigning in Ohio.

"I would like to promise and pledge to all of my voters and supporters and to all of the people of the United States that I will totally accept the results of this great and historic presidential election," he said. After pausing for several seconds, Trump added: "If I win."

Obama also said Trump's comments were further proof of the GOP candidate's unfitness to serve as president.

"All the Republicans - not all, but most - have acknowledged there's no way to rig an election in a country this big," Obama said. "He doesn't even worry if what he says is true. This is just about him worried that he's losing, which means he really doesn't have what it takes to hold this job."

Senator John McCain, the 2008 Republican candidate for president, also chastised Trump for trying to perpetrate the notion of a "rigged" election.

bik/jr (AP, AFP, Reuters)