North Korea has said it successfully performed another “crucial test” at its long-range rocket launch site that it claims will further strengthen its nuclear deterrent.

The test may have included technologies to improve intercontinental ballistic missiles (ICBMs) which could potentially reach the continental US.

The announcement, on Saturday, comes as North Korea continues to press the Trump administration for significant concessions as it approaches an end-of-year deadline set by its leader, Kim Jong-un, to salvage faltering nuclear negotiations.

North Korea’s Academy of Defence Science did not specify what had been tested on Friday. Days earlier, the North said it had conducted a “very important test” at the site, on the country’s north-western 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 US if Washington does not 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 which attended the test, carried out between 10.41 pm and 10.48pm on 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 one on 7 December, would 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 an analyst at Seoul’s Institute for Far Eastern Studies, said the North mentioning its nuclear deterrent made it clear it had 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 signalled a larger, liquid-fuel ICBM engine.

North Korea’s current ICBMs, including the Hwasong-15, are built with first stages 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.

The US president, Donald Trump, meets with the North Korean leader, Kim Jong-un, in Singapore on 12 June 2018. Photograph: Evan Vucci/AP

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 US mainland, raising tensions and triggering verbal warfare with Donald Trump as they exchanged crude insults and threats of nuclear annihilation. Experts say the North still needs to improve the missiles, such as ensuring that their warheads survive the harsh conditions of atmospheric re-entry, for them to be considered a viable threat.

Relations between Kim and Trump thawed 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 or how it would occur.

Negotiations faltered after the US 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. However, an October working-level meeting in Sweden broke down over what Pyongyang described as Washington’s “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 US persisted with sanctions and pressure against the North.

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 failed to make substantial concessions before the new year.

Some experts doubt that Kim would revive the tensions of 2017 by restarting nuclear and ICBM tests, which would cross a metaphorical “red line” and risk shattering his hard-won diplomacy with Washington. They say Kim is likely to pressurise Trump with military activities that pose less of a direct threat to the US and by bolstering a united front with Beijing and Moscow. Both are the North’s allies and have called for the UN security council to consider easing sanctions on Pyongyang to help nuclear negotiations move forward.