Seoul, South Korea – North Korea said Saturday it successfully performed another "crucial test" at its long-range rocket launch site that will 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. It suggests 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.

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.

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 lasted 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.

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The spokesman said the successful outcome of the latest test, in addition to the one on December 7, "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.

Kim Dong-yub, a former South Korean military officer and currently an analyst from Seoul's Institute for Far Eastern Studies, said the North mentioning its nuclear deterrent makes it clear it tested a new engine for an ICBM, not a satellite-launch vehicle. Kim said it was notable that North Korea announced the specific length of the test, which he said possibly signals a larger liquid-fuel ICBM engine.

North Korea's current ICBMs, including the Hwasong-15, are built with first stages that are powered by a pair of engines that experts say are modeled after Russian designs. When the North first tested the engine in 2016, it said the test lasted for 200 seconds and demonstrated a thrust of 80 tons-force.

The North Korean statement came a day before Stephen Biegun, the U.S. special representative for North Korea, was to arrive in South Korea for discussions with South Korean officials over the nuclear diplomacy. It also came after U.S. Ambassador Kelly Craft criticized the North's ballistic testing activity during a U.N. Security Council meeting on Wednesday, saying the tests were "deeply counterproductive" and risk closing the door on prospects for negotiating peace.

North Korea described her comments as a "hostile provocation" and warned that Washington may have squandered its chance at salvaging the fragile nuclear diplomacy.

During a provocative run of weapons tests in 2017, Kim Jong Un 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 a viable threat.