CARTILLIER (Canada) • US President Barack Obama warned against isolationist tendencies in America and elsewhere, calling it "the wrong medicine" to fix legitimate concerns about globalisation.

While he did not mention Mr Donald Trump by name, he took a clear swipe at the Republican presidential candidate's heated anti-trade rhetoric during a "Three Amigos" summit with his Canadian and Mexican counterparts.

"Even if we wanted to, we can't seal ourselves off from the rest of the world," Mr Obama said in a speech on Wednesday to the Canadian Parliament after trilateral talks.

"In an integrated, global economy, the solution is not for us to try to shut ourselves off from the world," he earlier told a news conference in Ottawa - held as Mr Trump repeated a threat to renegotiate or walk out of the North American Free Trade Agreement (Nafta), an accord that unites 530 million consumers and represents more than one-quarter of the world's gross domestic product.

Delivering a plea for regional cooperation and free trade, Mr Obama argued - in a thinly veiled rebuke to the real estate magnate - for growing the United States' relationship with Mexico, "our neighbour, our friend".

He accused some of exploiting fears by "arguing that we must rebuild walls and disengage from a chaotic world... in order to regain control of our lives". "We saw some of these currents at work this past week in the United Kingdom's referendum to leave the European Union," he said.

Mr Trump has made Mexicans a prime target of his anti-immigrant rhetoric, promising to build a wall on the US-Mexico border.

"We've had times throughout our history where anti-immigration sentiment is exploited by demagogues," said Mr Obama. "But guess what? They kept coming.

"Unless you are one of the first Americans, unless you are a native American, somebody, somewhere in your past showed up from some place else. And they didn't always have papers."

Mexican President Enrique Pena Nieto echoed Mr Obama's comments, saying "isolationism is not a road towards progress".

In the same vein, Canadian Prime Minister Justin Trudeau highlighted the joint efforts by the three nations, calling it "proof that cooperation pays off, and that working together always beats going it alone".

In the spirit of stepping up collaboration, the three leaders announced a strengthening of efforts to fight climate change.

The aim is to produce 50 per cent of the continent's overall electricity from clean energy, including from solar and wind, nuclear and hydroelectric generation, by 2025. This is up from 27 per cent last year.

Separately, Mr Obama will campaign with presumptive Democratic White House nominee Hillary Clinton for the first time next Tuesday, as a new poll shows a tightening race with Mr Trump.

The Democratic pair is scheduled to visit Charlotte, in the swing state of North Carolina, where they will "discuss building on the progress we've made and their vision for an America that is stronger together", Mrs Clinton's campaign said in a statement on Wednesday.

The presidential race is too close to call, with Mr Trump narrowing the gap with Mrs Clinton, according to the latest Quinnipiac University national poll. Respondents put Mrs Clinton ahead of Mr Trump by just 42 per cent to 40 per cent, a narrowing from Mrs Clinton's four- point margin in the organisation's June 1 survey.

The poll is considerably closer than the 12-point advantage for Mrs Clinton in Sunday's ABC News/Washington Post poll.

AGENCE FRANCE-PRESSE