North Korea says it has carried out a "very important test" at a satellite-launching site.
The KCNA state news agency said the results would be used to upgrade the country's strategic status. It provided no further details.
Analysts believe it could be a ground-based test of an engine to power a satellite launcher or an intercontinental ballistic missile.
It comes after Pyongyang appeared to shut the door on further US talks.
"We do not need to have lengthy talks with the US now, and denuclearisation is already gone out of the negotiating table," the North Korean envoy to the UN, Kim Song, said in a statement on Saturday.
North Korea had set an end-of-year deadline for the US to come up with a new denuclearisation deal that would involve significant sanctions relief and set it would otherwise adopt a "new path".
On Saturday, US President Donald Trump said he still hoped to reach an agreement.
Mr Trump made pursuing diplomacy with North Korea a centre-piece of his foreign policy agenda in 2018 but has failed to extract significant concessions on denuclearisation despite holding two summits with leader Kim Jong-un and even setting foot in North Korea.
The latest test took place at the Sohae satellite launch site, which the US once said Mr Kim had promised to close.
"The results of the recent important test will have an important effect on changing the strategic position of the DPRK [North Korea] once again in the near future," KCNA reported.
Despite facing a host of UN and other sanctions over its nuclear and misRead More – Source