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President Barack Obama said Thursday that world leaders are "rattled" by Donald Trump — and "for good reason."

During a press conference in Japan, Obama said the American presidential election is being "very" closely watched oversees. He told reporters that "it's fair to say" world leaders are "surprised" Trump is the presumptive Republican nominee.

"They are not sure how seriously to take some of his pronouncements but they're rattled by him — and for good reason, because a lot of the proposals that he's made display either ignorance of world affairs or a cavalier attitude," Obama added.

He suggested Trump's controversial proposals were more about "getting tweets and headlines" than "actually thinking through" what's needed to keep America safe or the "world on an even keel."

Trump has made China a frequent target of his attacks — such as saying the country will "suck the blood" out of the U.S.

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He also has said he wants to ban Muslims from entering the U.S., called the Iran deal "horrendous," pledged to "build a wall" along the Mexican border and that he'd have "no problem speaking to" North Korea's dictator.

Such a conversation would mark a major shift in U.S. policy towards Pyongyang — a country Obama earlier Thursday said was a "big worry."

North Korea's U.K. ambassador dismissed Trump's offer as "dramatics of a popular actors."

Trump also said he was unlikely to have a "very good relationship" with the U.K. — one of America's strongest allies — though later walked those comments back.

Obama spoke to reporters in Japan, where he on Friday will become the first sitting U.S. president to visit the Hiroshima Peace Park Memorial.

While he addressed the historic event in his opening remarks, questions quickly shifted to the U.S. election race.

Obama acknowledged the challenges of the long-running battle for the Democratic candidacy.

"During primaries people get grumpy with each other," Obama said.

He told reporters that he's sure the contenders wish the fight was over.

"It's a grind," he added.

As the race continues, a recent NBC News/Wall Street Journal Poll showed 61 percent of American voters said they were unsure about Trump's lack of military or government experience.

More than half of those polled — 56 percent — chose Democrat Hillary Clinton as the better candidate to handle foreign policy, compared to just 29 percent who picked Trump.

A lower total percentage of voters — 51 percent — expressed concern about Bernie Sanders potentially becoming the first self-described Democratic socialist to lead the country.