President Obama on Friday blasted Republican presidential front-runner Donald TrumpDonald John TrumpSchiff blasts Trump for making 'false claims' about Russia intel: 'You've betrayed America. Again.' Poll: Sanders leads 2020 Democratic field with 28 percent, followed by Warren and Biden More than 6 in 10 expect Trump to be reelected: poll MORE on an international stage for suggesting that countries like Japan and South Korea should have nuclear weapons. 

Trump’s statements reveal that the real estate magnate is unfit to serve as commander-in-chief, Obama said at a news conference at the Nuclear Security Summit in Washington.

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“They tell us that the person who made the statements doesn’t know much about foreign policy or nuclear policy or the Korean Peninsula or the world generally,” Obama said of Trump’s comments.

Earlier this week, Trump said nuclear weapons could help the two U.S. allies boost their ability to deter regional rivals like North Korea.

But Obama said it would be potentially fatal mistake if the country abandons its longtime stance that other nations should not acquire nuclear weapons. 

The president said the post-World War II peace forged by the United States and Japan and its alliance with South Korea have helped stave off another deadly conflict in the region and been a “boon” for American business and commerce in the Asia-Pacific. 

“You don’t mess with that,” Obama said. “We don’t want someone in the Oval Office who doesn’t understand how important that is.” 

Trump’s proposal was the latest example of how his international saber-rattling has roiled the presidential campaign. 

He told The New York Times over the weekend that Japan and South Korea should shoulder more of the expense of defending themselves against North Korea, whose nuclear ambitions have prompted renewed international concern. 

“There’ll be a point at which we’re just not going to be able to do it any more,” Trump said of the United States. “Now, does that mean nuclear? It could mean nuclear. It’s a very scary nuclear world.” 

The comments clearly frustrated Obama, who convened more than 50 world leaders for a two-day summit designed to find ways to reduce the number of nuclear weapons worldwide. 

The president said that Trump’s comments came up in his discussion with foreign leaders.  

“People pay attention to American elections,” he said. “Whatever do is really important to the rest of the world.  

“And even in those countries that are used to a carnival atmosphere in their own politics want sobriety and clarity when it comes to U.S. elections because they understand the president of the United States needs to know what’s going on around the world.”

Obama met with Japanese Prime Minister Shinzo Abe, South Korean President Park Geun-hye and Chinese President Xi Jinping on Thursday to discuss North Korea’s recent nuclear test and rocket launch.