President Barack Obama says that "loose talk" about Muslims by presidential hopeful Donald Trump and other Republicans is betraying American values and harming the fight against extremism

US President Barack Obama is tired of hearing Republican presidential candidate Donald Trump described as a populist.

The Democratic leader, who has made no secret of his dislike for the wealthy businessman's rhetoric, closed a news conference in Canada on Wednesday with a long riff on what makes a leader qualified for the "populist" mantra.

Trump did not meet the criteria, Obama said, without mentioning the Republican by name.

CHRIS WATTIE/REUTERS US President Barack Obama was in Canada at their House of Commons.

"Somebody ... who has never shown any regard for workers, has never fought on behalf of social justice issues or making sure that poor kids are getting a decent shot at life or have health care," does not meet the definition, Obama said.

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HANDOUT Canadian Prime Minister Justin Trudeau takes a selfie with US President Barack Obama.

"They don't suddenly become a populist because they say something controversial in order to win votes. That's not the measure of populism. That's nativism, or xenophobia. Or worse. Or it's just cynicism," he said.

Trump won enough grassroots support among Republicans to make him the party's presumptive presidential nominee with a pledge to ban Muslims temporarily from entering the United States and to build a wall on the U.S. border with Mexico, and a series of other inflammatory remarks.

Obama has sharply criticised Trump for such rhetoric.

He plans to campaign with former Secretary of State Hillary Clinton, the presumptive Democratic presidential nominee, next week. The president's latest criticism of Trump could foreshadow Obama's strategy to help Clinton on the campaign trail.

He made a point of saying US Senator Bernie Sanders of Vermont, Clinton's opponent in the race for the Democratic presidential nomination, genuinely deserved the title of populist.

Sanders describes himself as a democratic socialist and generated huge support from young people across the United States in his campaign.

Clinton needs those supporters now, and Obama, who won the White House in 2008 and 2012 with a similar coalition, will try to help deliver them for her.

Obama, who leaves office in January, made his comments on Wednesday (Thursday NZT) with Canadian Prime Minister Justin Trudeau and Mexican President Enrique Pena Nieto looking on.

"Sorry," Obama said after his more-than-six-minute monologue. "It's the prerogative of an outgoing president to go on an occasional rant, he said.