WASHINGTON -- US President Donald Trump said Sunday that North Korean leader Kim Jong-un could lose "everything" if he acts in a hostile manner, sending a clear warning to the regime to refrain from provocations such as nuclear and missile tests.

Trump sent the tweet as the two countries have exchanged heated rhetoric over their stalled negotiations on dismantling Pyongyang's nuclear weapons program.

Earlier Sunday, North Korea said it had conducted an unexplained "very important test" at its Dongchang-ri satellite launching site, prompting speculation of preparations for a new long-range missile test.

But the US president also signaled his commitment to continuing diplomacy with Kim, saying the North Korean leader is "too smart" to be rash.

"Kim Jong-un is too smart and has far too much to lose, everything actually, if he acts in a hostile way," the US president wrote.

"He signed a strong Denuclearization Agreement with me in Singapore. He does not want to void his special relationship with the President of the United States or interfere with the US Presidential Election in November. North Korea, under the leadership of Kim Jong Un, has tremendous economic potential, but it must denuclearize as promised. NATO, China, Russia, Japan, and the entire world is unified on this issue!" he added.

Trump and Kim held their first summit in Singapore in June 2018 and agreed to "work toward" complete denuclearization of the Korean Peninsula in exchange for US security guarantees.

There has been little progress in implementing the deal as the two sides remain apart on how much the North should denuclearize in order to receive sanctions relief and other concessions from the US.

Kim has set the end of the year as the deadline for the negotiations, warning the regime could seek a "new way" if the US fails to come up with an acceptable offer.

The warning has been interpreted as a threat to restart tests of nuclear weapons and intercontinental ballistic missiles, which the North has suspended since resuming diplomacy with the US in earnest in early 2018.

Trump has touted the absence of such tests as one of his major diplomatic victories, and their resumption could hurt his reelection campaign.

He told reporters Saturday he'd be "surprised" if North Korea acted in a hostile way.

"He knows I have an election coming up," Trump said, referring to Kim. "I don't think he wants to interfere with that. But we'll have to see."

Last week, Trump hinted that the US will use military force against North Korea if necessary. The North Korean regime responded angrily, saying it will take "prompt corresponding actions at any level" if forced.

The North also urged the US last week to do its part to salvage the negotiations, warning it is entirely up to the US what "Christmas gift" it will get.

It also announced plans to convene a key meeting of the ruling Workers' Party at an unspecified date later this month to decide on "crucial issues," a possible reference to forthcoming policy changes regarding negotiations with Washington. (Yonhap)