"I feel it is high time to surely break with the south Korean authorities. We will soon take a next action," she said in the latest denunciation of Seoul.

Since last week the North has issued a series of vitriolic condemnations of the South over activists sending anti-Pyongyang leaflets over the border -- something defectors do on a regular basis.

"By exercising my power authorized by the Supreme Leader, our Party and the state, I gave an instruction to the arms of the department in charge of the affairs with enemy to decisively carry out the next action," said Kim Yo Jong, who is a key advisor to her brother.

She added that "the right to taking the next action against the enemy will be entrusted to the General Staff of our army."

Kim did not elaborate on what the military action would be but appeared to threaten the destruction of the Joint Liaison Office, in the North Korean border city of Kaesong.

"Before long, a tragic scene of the useless north-south joint liaison office completely collapsed would be seen," her statement on KCNA said.

Last week she condemned Seoul for not blocking activists from flying balloons carrying anti-regime leaflets across the border.

Pyongyang has since issued a series of statements and held several citizens' rallies railing against the South, with KCNA describing leaflet scattering as "an act of a preemptive attack that precedes a war".

"It is necessary to make them keenly feel what they have done," said Kim Yo Jong, referring to what she called the South's failure to stop the leaflet campaign.

It was the second angry outburst from Pyongyang on Saturday. Earlier in the day, the North excoriated the South for making "nonsensical talking" about the denuclearisation process and trying to "meddle" in the US-North talks.

Inter-Korean ties have been at a standstill since the collapse of the second US-North summit in Hanoi in February last year, with a deadlock over the concessions Washington was willing to offer in return for Pyongyang's denuclearisation measures.

Saturday's broadside came a day after Pyongyang issued a stinging denunciation of the United States on the second anniversary of a landmark summit in Singapore where President Donald Trump shook hands with North Korean leader Kim Jong Un.

It contained some of the harshest criticism Pyongyang has sent Washington's way in recent months and cast doubts over the future of the long-deadlocked nuclear talks process.