Washington (AFP) - Toughening immigration checks for the French and Germans, questioning NATO obligations and hinting at an exit from the World Trade Organization: Donald Trump cast further doubt Sunday on US alliances and commitments around the world.

In his first wide-ranging interview since he was crowned the Republican Party's White House nominee, the billionaire and political novice spelled out his stance on a slew of foreign policy, international trade and national security issues.

If he wins in November, he told NBC's "Meet the Press," France and other nations hit by recent terror attacks would be subjected to "extreme" immigration checks as a deterrent to attacks on US soil.

Trump recently shifted from calling for a ban on Muslims entering the United States to advocating freezing flows from what he calls countries "compromised by terrorism."

"We have problems in Germany and we have problems in France," he said, arguing that in his view the French "have totally been" compromised by deadly Islamist attacks in Nice and last year in Paris.

"And you know why? It's their own fault. Because they allowed people to come into their territory."

Asked about the risk his proposal could drastically limit the number of people allowed into the US, Trump said: "Maybe we get to that point," adding: "We have to be smart and we have to be vigilant and we have to be strong."

- 'WTO is a disaster' -

Beyond questioning free travel from Europe to the United States, Trump put forward a vision of Europe as an economic competitor to be bested at all costs.

Asked, in relation to the British vote to leave the European Union, whether a fractured Europe was good for America, Trump equivocated.

"No, no -- but we're spending a lot of money in Europe," he said. "Don't forget, Europe got together, why primarily did they get together? To beat the United States when it comes to making money. In other words, on trade.

"Look at Airbus," he said. "They got together, all of these countries got together so they could beat the United States. Okay?"

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Trump, who has already threatened to renegotiate or rip up the North American Free Trade Agreement, went on to suggest that the United States could pull out of the World Trade Organization under his presidency.

In the interview, he put forward a plan for punitive import taxes of up to 30 percent on firms that move manufacturing activities abroad, citing NAFTA partner Mexico as an example.

When show host Chuck Todd objected that such plans would be challenged at the WTO, he responded:

"Doesn't matter. We'll renegotiate or pull out. These trade deals are a disaster, Chuck. World Trade Organization is a disaster."

Asked if he was concerned such actions could rattle the world economy -- much as the Brexit vote has done -- Trump was dismissive.

"I'm the only one that said Brexit is going to happen," he said. "What did it do? The stock market is higher now than when it happened."

- 'Taking advantage of us' -

Trump doubled down on a recent warning that the US might not meet its mutual defense obligations in NATO under his presidency -- if he deemed that a member state was not pulling its weight financially.

President Barack Obama weighed in, questioning Trump's readiness to be commander-in-chief in an interview on CBS.

"Anybody who's been paying attention knows there is a big difference between challenging our European allies to keep up their defense spending, particularly at a time when Russia's been more aggressive, and saying to them, 'You know what? We might not abide by the central tenet of the most important alliance in the history of the world,'" Obama said.

Pressed on the issue by Todd, Trump was unapologetic, repeating that he would make allies shoulder defense costs that the United States has borne for decades.

"Now, a country gets invaded. They haven't paid. Everyone said 'Oh, but we have a treaty'."

"We have countries within NATO taking advantage of us. With me, I believe they are going to pay," he said.

"If they don't pay -- Chuck -- this isn't 40 years ago. This isn't 50 years ago. It's not 30 years ago. We're a different country today."

Trump said his demands for a review of defense spending by US allies would go beyond NATO.

"We take care of Japan. We take care of Germany and South Korea and Saudi Arabia and we lose on everything," he said.

"We can no longer be the stupid country."