North Korean state media has said Kim Jong-un supervised the test-firing of a new guided weapons system to improve the country's tactical nuclear weapons.
It follows days of celebrations surrounding the birthday of his grandfather and founding leader, Kim Il-sung.
The launch was the latest in an unprecedented blitz of weapons tests this year, in violation of sanctions, which included firing an intercontinental ballistic missile at full range for the first time since 2017.
It also came just ahead of US-South Korea military training exercises - which have always infuriated Pyongyang due to begin tomorrow.
The North's official KCNA news agency reported that the "new-type tactical guided weapon... is of great significance in drastically improving the firepower of the frontline long-range artillery units and enhancing the efficiency in the operation of tactical nukes."
It said the test was successful, but did not specify when or where it took place.
South Korea's Joint Chiefs of Staff said it detected two projectiles fired late on Saturday, which flew 110 kilometres at an altitude of 25 kilometres, travelling at speeds of around Mach 4 - some 4,800km per hour.
A Pentagon spokesperson said the United States was "aware of the North Korean statement that they conducted a test of a long range artillery system", adding it was monitoring.
Analysts had widely expected Pyongyang could conduct a nuclear test as part of events to celebrate Friday's anniversary of the 110th birthday of North Korea's founding leader.
Expectations were heightened because of indications that Pyongyang had restarted work at one of its known nuclear testing sites.
Analysts said the weapon tested over the weekend appeared to be a new short-range ballistic missile - but no less significant.
Ankit Panda, a senior fellow at the Carnegie Endowment for International Peace said: "This is North Korea's first tactical nuclear weapon delivery system, it would seem.
"You don't have to be particularly imaginative to put this two and two together."
Photos carried by the Rodong Sinmun newspaper showed a grinning Kim surrounded by uniformed officials applauding as he watched what it said was the test-firing of the weapon.
According to state media, Mr Kim gave a military research team "important instructions on further building up the defence capabilities and nuclear combat forces."
He had also overseen in Pyongyang a series of events to celebrate Friday's anniversary, including a huge civilian parade, mass dance parties, and fireworks - but no military parade to show off the regime's new weapons.
