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In a tweet, Trump sticks North Korea’s Kim Jong Un with a nickname: ‘Rocket Man’

A submarine-launched ballistic missile is displayed in Kim Il Sung Square during a military parade in April in Pyongyang, North Korea, to celebrate the 105th birth anniversary of Kim, the country's late founder. (Wong Maye-E/AP)

NEW YORK — President Trump is calling Kim Jong Un names — the “Rocket Man.”

The president stuck the moniker on the North Korea dictator in a Sunday morning tweet ahead of Trump's scheduled arrival here in the evening for the U.N. General Assembly, the annual gathering of more than 120 world leaders.

Trump, who has spent two nights at his golf resort in Bedminster, N.J., also revealed that he spoke with South Korean President Moon Jae-in, who will join Trump and Japanese Prime Minister Shinzo Abe for a trilateral dinner this week in New York to collaborate on addressing North Korea's growing nuclear and ballistic missile threats. The White House said Trump and Moon discussed North Korea’s continued defiance of the international community and “committed to continuing to take steps to strengthen deterrence and defense capabilities and to maximize economic and diplomatic pressure.”

The president's Twitter snark came two weeks after Kim's regime undertook its biggest nuclear test to date, an explosion that analysts estimate at 250 kilotons, nearly 17 times the size of the atomic bomb that devastated Hiroshima in 1945. Radar satellite images show the test was powerful enough to sink a roughly 85-acre area on the peak of a mountain above the tunnels where the test is thought to have taken place.

On CBS's “Face the Nation” Sunday morning, Secretary of State Rex Tillerson said the U.S. strategy is to deny North Korea nuclear weapons and the ability to deliver them, but stressed that the contest is what he called the “four nos.”

“The four nos being that we do not seek regime change, we do not seek a regime collapse, we do not seek an accelerated reunification of the peninsula, and we do not seek a reason to send our forces north of the demilitarized zones,” Tillerson said.

If diplomacy fails to coerce North Korea to the negotiating table, he said, “our military option will be the only one left. So all of this is backed up by a very strong and resolute military option. But be clear, we seek a peaceful solution to this”

Tillerson said the message is designed to bring about cooperation from China, as well as addressing the country's fears that a regime collapse would flood their border with refugees. China facilitates about 90 percent of North Korea's trade and provides its oil supplies.

Trump said Thursday that he's working with China to continue to exert more pressure on Pyongyang, but he declined to elaborate.

“We are working on different things.  I can't tell you, obviously, what I’m working on. But believe me, the people of this country will be very, very safe,” Trump told reporters. “I think that a lot of effort is being put into this. We're looking at what’s going on. As we speak, we are literally at it right now, and you will be seeing what we’ll be doing.”

North Korea's growing ability to potentially reach the continental United States with a ballistic missile, which could be mounted with a miniature nuclear device, has increased the urgency for the Trump administration. The U.S. ambassador to the United Nations, Nikki Haley, pointed to the world body's two recent votes to impose more severe economic sanctions on the North as signs that the international community is united in its condemnation.

“North Korea is pretty much cut off from the world,” she said on CNN's “State of the Union” on Sunday. But she added that military options remain on the table: “If North Korea keeps on with this reckless behavior and if the U.S. has to defend itself or its allies in any way, North Korea will be destroyed. We don’t want that. We don’t want war. But something is going to have to be done.”

Tillerson stressed Sunday that the threat is growing as North Korea advances its technology and capability. "We've said from the beginning, we don't have a lot of time left," he said. We don't have a runway left to land this plane on.”