"Today, I hope I speak not only for our countries, but for all civilized nations, when I say to the North: Do not underestimate us. And do not try us,” the president said during a speech to South Korea’s National Assembly.

Trump used his address to send a message to North Korean leader Kim Jong Un, telling him “the weapons you are acquiring are not making you safer, they are putting your regime in grave danger.”

He urged countries around the world to take drastic measures to isolate Pyongyang in order to bring an end to its nuclear program.

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“All responsible nations must join forces to isolate the brutal regime,” Trump said. “You cannot support, you cannot supply, you cannot accept.”

Wrapping up a two-day visit to South Korea, Trump revived his tough talk against North Korea and Kim, whom he has previously dubbed “little Rocket Man.”

"We will not allow American cities to be threatened with destruction,” he said. “We will not be intimidated. And we will not let the worst atrocities in history be repeated here, on this ground we fought and died so hard to secure."

The remarks came one day after Trump appeared to dial back his combative rhetoric, saying that the aggressive steps taken by the U.S. and its allies were designed to create conditions to “make a deal" with North Korea.

Trump was denied the chance to punctuate his warnings with a symbolic visit to the heavily fortified Demilitarized Zone separating North and South Korea.

Just hours before the speech, the president attempted to make a surprise visit to the tension-filled border area, but was forced to turn back due to bad weather.

Trump’s words will likely attract attention in China, where the president is traveling later Wednesday .

White House officials have said Trump will use his talks with Chinese President Xi Jinping to pressure him to do more to isolate North Korea.

China is North Korea’s largest trading partner and Trump has depended on Xi to exert leverage on the rogue nation.

The president said nations should abide by U.N. economic sanctions against North Korea, sever trade ties and downgrade diplomatic relations with Pyongyang.