The North hasn't publicly tested any weapons since November 2017, but in recent days Pyongyang reportedly expressed anger at US -led worldwide sanctions and ongoing small-scale military drills between South Korea and the United States.
After a series of provocative nuclear and missile tests last year that fueled fears of war, North Korea entered talks with the United States and South Korea early this year with a vague commitment to nuclear disarmament.
Talks between the two capitals look unlikely to resume with any oomph until Kim and Trump meet for their second summit in the new year.
The State Department downplayed the news. "North Korea is saying 'If you don't listen to us, you will face political burdens, '" said analyst Shin Beomchul of Seoul's Asan Institute for Policy Studies.
'We are talking with the North Koreans about implementing all of those commitments.
He stressed that President Donald Trump is "still grateful" for the Republic's hosting of the Trump-Kim summit in June 2018.
South Korea's defense ministry said it did not have an immediate comment but was preparing a statement on the North Korean test.
'It's not appropriate for our military to view it as a provocation when North Korea has confirmed it is a high-tech tactical weapon test, ' he added.
Kim reportedly said that the new weapons system was one that his father, Kim Jong-il, was especially interested in during his lifetime, having led the development personally.
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Jong-un expressed "great satisfaction" and said the test marked a "decisive turn in bolstering the fighting capacity" of the North's military, KCNA said.
"The testing of the high-tech tactical weapon has been carried out successfully". South Korea's Transportation Ministry said North Korea on Friday proposed connecting worldwide air routes along the western and eastern coasts of the peninsula during working-level talks on aviation cooperation. 'But North Korea announced it publicly to show its frustration'.
The news came nearly a year after Pyongyang's last test of an intercontinental ballistic missile and recalled the repeated announcements of 2017, which included by far its most powerful nuclear blast to date and rockets that brought the whole of the U.S. mainland into range.
Those included by far North Korea's most powerful nuclear blast to date and rockets that brought the whole of the USA mainland into range.
It is rare for North Korea to release an American detainee so swiftly and it comes amid stalled negotiations over Pyongyang's nuclear programme.
Kim this year declared his nuclear force "complete" and said he would focus on economic development.
Diplomacy has stalled since the Singapore summit, with Washington pushing for more action on nuclear disarmament and the North insisting that the USA first approve a peace declaration formally ending the Korean War and lift sanctions.
But Pyongyang is demanding sanctions imposed against it over its weapons programmes are eased and has condemned USA demands for what it calls its "unilateral" disarmament as "gangster-like".
Washington insists the measures should stay in place until the North's "final, fully verified" denuclearization.
"This gesture means the North wants to keep up momentum for dialogue with the United States", professor Yang Moo-Jin at the University of North Korean Studies told AFP.