TOKYO — North Korea announced Saturday it had conducted another test at a satellite launch station near the Chinese border, saying the unspecified test would help bolster the country's nuclear deterrent.

The test was conducted Friday evening, and it was the second in less than a week at the Sohae Satellite Launching Station in Tongchang-ri, a site near the Chinese border that has been used to test rocket engines and launch satellites into space in the past.

The test lasted from 22:41 to 22:48 local time, the statement said, in what could be a reference to a rocket-engine test, similar to the one that experts concluded had been carried out six days before.

“The research successes being registered by us in defense science one after another recently will be applied to further bolstering up the reliable strategic nuclear deterrent of the Democratic People’s Republic of Korea,” a spokesman for North Korea’s Academy of National Defense Science said in a statement.

The explicit linkage of the test to North Korea’s nuclear weapons arsenal marks another escalation in Pyongyang’s rhetoric as it threatens to withdraw from dialogue with the United States and potentially renege on a pledge to stop testing nuclear weapons and inter-continental ballistic missiles — unless it gets concessions before a year-end deadline.

It has threatened to deliver an unwelcome “Christmas gift” to the United States, something experts say could mean an ICBM test, a satellite launch or simply a formal decision to break off denuclearization talks with Washington.

But state media made no mention of North Korean leader Kim Jong Un attending the test, instead saying defense scientists “were greatly honored to receive warm congratulations from the Central Committee of the Workers’ Party of Korea on the spot.”

Kim has not been reported as attending any recent tests explicitly linked to North Korea’s nuclear deterrent, noted Ankit Panda, a North Korea expert at the Federation of American Scientists.

Stephen Biegun, the U.S. special envoy for North Korea, will arrive in Seoul on Sunday for a three-day visit aimed at keeping the dialogue with Pyongyang alive, South Korea’s foreign ministry announced Friday. He will then travel to Tokyo to meet Japanese officials.

On Thursday, North Korea’s foreign ministry issued another angry denunciation of the United States, especially of Washington’s criticism of its weapons tests at the United Nations Security Council.

“If bolstering of military capabilities for self-defense should be termed an act of destroying global peace and security, there comes the conclusion that all the steps taken by other countries for bolstering up their defense capabilities should be taken issue with,” a foreign ministry spokesman said in a statement.

“Such claims that they are entitled to launch ICBMs any time and we are not allowed to conduct the tests done by any other countries just sheds light on the nature of the bandit-like U.S. which seeks to disarm us completely.”

State media says Kim will make a big decision before the end of this year on the country’s strategic direction, and the foreign ministry said U.S. criticism “decisively helped us make a definite decision on what way to choose.”

It is unlikely Biegun’s visit will change that calculation, experts said.

“I think we have a good idea of which way Kim is going if he was making his mind up between an ostensibly civilian space launch or a highly provocative intercontinental-range ballistic missile launch,” said Panda, author of a forthcoming book “Kim Jong Un and the Bomb.”

“Today’s test is further evidence that he is leaning toward the latter.”

Van Jackson, a former Pentagon official who now teaches at Victoria University in New Zealand, called the test a “calibrated escalation” along a pretty predictable trendline, with Kim encouraged by President Trump to believe he can obtain sanctions relief without surrendering any meaningful part of his nuclear deterrent.

Jackson said Kim had been allowed to conduct diplomacy on his own terms last year, launching a charm offensive after securing a good-enough nuclear deterrent in late 2017.

“The very fact that Kim is trying to coerce the U.S. is proof that he thinks he has a strong bargaining hand. So if he doesn’t get what he wants, given his strong hand, he’ll escalate. And escalate. Until he gets what he wants,” he said.

“The latest test falls along that escalation ladder. So the U.S. has to ask where this ends because this is going in a predictably explosive direction. We’re headed toward another nuclear crisis, and we’re largely responsible for it.”