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.

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.

The spokesman said the successful outcome of the latest test, in addition to the one on Dec. 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 modelled 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.