Unspecified test comes after South Korea think-tank’s warning that Pyongyang may end nuclear talks later this month.

North Korea has announced it successfully performed another “crucial test” at its long-range rocket launch site that would further strengthen its “reliable strategic nuclear deterrent”.

The announcement on Saturday came as Pyongyang continued to pressure the Trump administration over 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, North Korea said it had conducted a “very important test” at the site, prompting speculation that it involved a new engine for either a space launch vehicle or an intercontinental ballistic missile.

North Korea has been demanding the United States make concessions to break the deadlock in their nuclear negotiations.

In the last few weeks, Pyongyang carried out at least 13 ballistic missile launches that began in May.

Pyongyang has also promised an ominous “Christmas gift” if the US does not come up with concessions by the end of the year.

Kim has also held three meetings with US President Donald Trump since June 2018 but little progress has been made in efforts towards denuclearisation since then.

On Friday, the South Korean news agency, Yonhap, quoted the Institute for National Security Strategy that Pyongyang could announce the end of the nuclear talks later this month.

The institute is affiliated with South Korea’s spy agency.

“For the time being, [the North] is expected to take low-intensity steps, such as resuming nuclear activities or repairing rocket launching sites, but if [the North] takes action, it would be done in a way to demonstrate its strategic position,” the think-tank was quoted by Yonhap as saying.