North Korea has conducted a "crucial test" at a satellite launch site to boost its nuclear deterrent, state media report.
A spokesman told KNCA news agency it took place late on Friday at the Sohae Satellite Launching Ground, but did not give specific details.
Talks between the US and North Korea about its nuclear programme remain stalled.
US President Donald Trump has refused to lift biting sanctions until North Korea fully abandons its nuclear programme.
North Korea has stepped up its weapons tests and its strong rhetoric in recent weeks, and leader Kim Jong-un has been asking for new concessions from the US by the end of the year.
Pyongyang has said it will adopt a "new way" if that does not happen - saying the US can expect an ominous "Christmas gift" if it does not comply.
What was the test?
It is not clear exactly what North Korea tested at the site.
Ankit Panda, North Korea expert at the Federation of American Scientists, told the BBC it could be a ground test for a ballistic missile engine. South Korea's defence minister had described that as the purpose of the previous test in December.
After Saturday's test, North Korea's Chief of the General Staff Pak Jong Chon warned "hostile forces" that they should not provoke his country, according to state media.
Last month, Japan condemned Pyongyang for "repeated launches of ballistic missiles" after two projectiles were fired.
The North however said it was testing a "super-large multiple-rocket launcher", and threatened that Japan "may see what a real ballistic missile is in the not distant future".
Why is North Korea conducting a test now?
The test comes amid heightening tensions in the region.
The UN Security Council met on Wednesday at the request of the US to discuss North Korea's weapons programme - a move North Korea called a "serious provocation".
And on Sunday, US Special Representative for North Korea Stephen Biegun will arrive in the South Korean capital Seoul for a three-day visit, where they are expected to discuss recent developments and denuclearisation.
US President Donald Trump has said he still hopes to reach an agreement with North Korea.
The president 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 briefly setting foot in North Korea.
The US tested a medium-range ballistic missile over the Pacific Ocean on Thursday - a weapon that would have been prohibited under the 1987 Intermediate-Range Nuclear Forces Treaty which President Trump left earlier this year.