SEOUL, South Korea — North Korea said Saturday it successfully performed another “crucial test” at its long-range rocket launch site that would further strengthen its nuclear deterrent.

The test possibly involved technologies to improve intercontinental ballistic missiles that could potentially reach the continental United States.

The announcement comes as North Korea continues to pressure the Trump administration for major concessions as it approaches an end-of-year deadline set by leader Kim Jong Un to salvage faltering nuclear negotiations.

North Korea’s Academy of Defense Science did not specify what was tested on Friday.

Just days earlier, the North said it conducted a “very important test” at the site on the country’s northwestern coast, prompting speculation that it involved a new engine for either an ICBM or a space launch vehicle.

The announcement suggests that the country is preparing to do something to provoke the United States if Washington doesn’t back down and make concessions to ease sanctions and pressure on Pyongyang in deadlocked nuclear negotiations.

Chief of the General Staff Pak Jong Chon warned that "hostile forces," including the United States, should refrain from provoking North Korea if they wanted to see a peaceful New Year, state news agency KCNA said.

An unnamed spokesman for the academy said scientists received warm congratulations from members from the ruling Workers’ Party of Korea Central Committee who attended the test that was conducted from 10:41 to 10:48 p.m. Friday at the Sohae Satellite Launching Ground, where the North has conducted satellite launches and liquid-fuel missile engine tests in recent years.

The spokesman said the successful outcome of the latest test, in addition to the one last Saturday, “will be applied to further bolster up the reliable strategic nuclear deterrent of the Democratic People's Republic of Korea,” referring to North Korea’s formal name.

During a provocative run in weapons tests in 2017, Kim conducted three flight tests of ICBMs that demonstrated potential range to reach deep into the U.S. mainland, raising tensions and triggering verbal warfare with President Donald Trump as they exchanged crude insults and threats of nuclear annihilation.

Experts say that the North still needs to improve the missiles, such as ensuring that their warheads survive the harsh conditions of atmospheric reentry, for them to be considered as a viable threat.

Relations between Kim and Trump became cozier in 2018 after Kim initiated diplomacy that led to their first summit in June that year in Singapore where they issued a vague statement on a nuclear-free Korean Peninsula, without describing when and how it would occur.

But negotiations faltered after the United States rejected North Korean demands for broad sanctions relief in exchange for a partial surrender of the North’s nuclear capabilities at Kim’s second summit with Trump in Vietnam in February.

Trump and Kim met for a third time in June at the border between North and South Korea and agreed to resume talks. But an October working-level meeting in Sweden broke down over what the North Koreans described as the Americans’ “old stance and attitude.”

Kim, who unilaterally suspended nuclear and intercontinental ballistic missile tests last year during talks with Washington and Seoul, has said North Korea could seek a “new path” if the United States persists with sanctions and pressure against the North.

....with the U.S. 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! — Donald J. Trump (@realDonaldTrump) December 8, 2019

North Korea has also conducted 13 rounds of ballistic missile and rocket artillery tests since May, and has hinted at lifting its moratorium on nuclear and long-range missile tests if the Trump administration fails to make substantial concessions before the new year.

Saturday's news of the test came after U.S. Ambassador Kelly Craft on Wednesday criticized the North’s ballistic testing activity during a U.N. Security Council meeting, saying that the tests were “deeply counterproductive” and risk closing the door on prospects for negotiating peace.

She also cited North Korean hints of “a resumption of serious provocations,” which she said would mean they could launch space vehicles using long-range ballistic missile technology or test ICBMs, “which are designed to attack the continental United States with nuclear weapons.”

While Craft said that the Trump administration is “prepared to be flexible” and take concrete, parallel steps toward an agreement on resuming talks, North Korea described her comments as a “hostile provocation” and warned that Washington may have squandered its chance at salvaging the fragile nuclear diplomacy.