Trump warns North Korea's Kim Jong Un not to put their 'special relationship' at risk with 'hostile' acts

President Donald Trump warned North Korean leader Kim Jong Un that he could be putting their "special relationship" at risk if his regime begins to behave aggressively or abandon its commitment to denuclearization.

"Kim Jong Un is too smart and has far too much to lose, everything actually, if he acts in a hostile way," Trump said in a tweet. "He does not want to void his special relationship with the President of the United States or interfere with the U.S. Presidential Election in November."

North Korean announced Sunday that it conducted a "very important test" at a long-range missile site, which was partially dismantled last year in a step Trump had hailed as evidence of the regime's commitment to denuclearization after his first summit with Kim.

Trump reminded Kim of his commitment on Sunday and said his regime "must denuclearize as promised."

"NATO, China, Russia, Japan, and the entire world is unified on this issue!" Trump said.

After that first meeting in Singapore in June 2018, Trump proudly announced that Kim had agreed to the "complete denuclearization" of the Korean Peninsula and that he was "already destroying a major missile engine testing site."

Satellite imagery showed that a rocket-engine testing stand was among the structures that were dismantled at the Sohae Satellite Launching Ground, which experts believe a center for the development of engines for intercontinental ballistic missiles, after the Singapore summit. But in March, South Korean intelligence reported that work was underway to make the site functional again.

More: North Korea gives fiery reply to Trump after president's 'undesirable remarks'

Saturday's "successful test" was of "great significance" and will have "an important effect on changing the strategic position" of North Korea, an unidentified spokesman from the North’s Academy of National Defense Science said in a statement carried by the country’s official Korean Central News Agency.

The North offered no details about the nature of the test. Kim Dong-yub, an analyst at Seoul’s Institute for Far Eastern Studies, told the Associated Press that it may have been the regime's first test of a solid-fuel engine for an intercontinental ballistic missile. Its previous rockets used liquid fuels, and a switch to solid fuels would increase mobility while cutting the time needed for a launch.

Trump has touted his relationship with Kim and expressed optimism that negotiations could lead North Korea to give up its nuclear weapons program. But at their second summit, which took place February in Hanoi, the two sides reached an impasse, and since then the talks have remained deadlocked.

More: Trump says he still gets along with Kim Jong Un, despite North Korea's criticism

In April, Kim said his regime would seek a "new path" if the U.S. did not offer more in terms of sanction reduction before the end of the year. In recent months, North Korea has conducted several missiles tests and has repeatedly reminded the U.S. of Kim's end-of-year deadline.

On Saturday, the regime's ambassador to the United Nations, Kim Song, said that denuclearization "had already gone out of the negotiation table" and that the Trump administration was following a "hostile policy" meant to "stifle" the regime.

When asked Sunday how the U.S. would respond if Kim resumes nuclear testing and the launching of long-range missiles, Defense Secretary Mark Esper told "Fox News Sunday" host Chris Wallace that he didn't want to address a hypothetical scenario but that his job was to "ensure that we are ready" and "prepared to fight and win tonight, if necessary."

"We are in a high state of readiness right now," Esper said.

But he stressed the importance of diplomacy and said, "The talks are always open."

"We want to have negotiations," Esper said. "We want to reach the point where we have denuclearized North Korea."

During an interview on CBS News' "Face the Nation" on Sunday, national security adviser Robert O'Brien said he still thought Kim wanted to honor his commitment to denuclearize and warned resuming nuclear test "would be a mistake on the part of North Korea."

Echoing his tweets on Sunday, Trump told reporters Friday at the White House: "I'd be surprised if North Korea acted hostilely. I have a very good relationship with Kim Jong Un. He knows I have an election coming up. I don't think he wants to interfere with that."

Contributing: The Associated Press

This article originally appeared on USA TODAY: North Korea: 'Important test' conducted at once dismantled Sohae site