Barack Obama. AP President Barack Obama on Tuesday threw cold water on Donald Trump's recent unfounded claims that the general election has already been "rigged" against him.

"I've 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," Obama said during a press conference at the White House with Italian Prime Minister Matteo Renzi.

Calling Trump's claims "unprecedented" and "based on no facts," Obama emphasized that there was no evidence of widespread election and voter fraud. He said "no serious person" could rig an election in the US if they tried.

The president noted that Florida, with its Republican-controlled election system, demonstrated the US's purposefully decentralized election system, which places control of elections in the hands of state and local officials, making widespread fraud unlikely and cumbersome.

"The notion that somehow if Mr. Trump loses Florida it's those people you have to watch out for? That is both irresponsible, and by the way, doesn't really show the leadership and toughness you'd want to see in a president," Obama said. "You start whining before the game's even over?"

He added: "I'd advise Mr. Trump to stop whining and go make his case to get votes."

The president also laid out the case that if Trump won the election, he would expect Democratic nominee Hillary Clinton to concede. He said he would dutifully carry out the transition of power between his administration and that of Trump if the real-estate mogul were elected.

Obama's rebuke comes as Trump and many of his top campaign surrogates have increasingly made the unfounded case that there is a widespread conspiracy in the media to "rig" the election against Trump.

"Of course there is large scale voter fraud happening on and before election day," Trump tweeted Monday morning. "Why do Republican leaders deny what is going on? So naive!"

Republican leaders like House Speaker Paul Ryan, as well as several other Trump-supporting state leaders in swing states, have also rebuked their nominee and worked to assure voters that there would be no election fraud.