SEOUL • North Korea said yesterday that 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 (ICBM) 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 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 congratulations from members of the ruling Workers' Party of Korea central committee who attended the test that lasted from 10.41pm to 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 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.

Mr Kim Dong-yub, a former South Korean military officer and currently an analyst at 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. Mr 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.

The North Korean statement came a day before Mr Stephen Biegun, the US Special Representative for North Korea, was to arrive in South Korea for discussions with officials over nuclear diplomacy. It was unclear whether Mr Biegun would attempt contact with North Korean officials at the inter-Korea border.

During a provocative run of weapons tests in 2017, Mr 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 US President Donald Trump.

Experts say that the North still needs to improve the missiles for them to be considered a viable threat.

Relations between Mr Kim and Mr Trump became cosier after their first summit in June last year in Singapore, where they issued a vague statement on a nuclear-free Korean Peninsula, without describing when or how it would occur. But 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 Mr Kim's second summit with Mr Trump in Vietnam in February.

Both leaders 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".

ASSOCIATED PRESS