On Saturday, Pyongyang delivered an ultimatum to Seoul demanding it stop broadcasting propaganda via loudspeakers across the borders. It set a deadline of 17:00 local time (08:00 GMT) on Saturday for this to happen. The North threatened ‘imminent’ military action if Seoul didn’t meet the demands.
However, South Korean Vice Defense Minister Baek Seung-joo told parliament that the broadcasts would continue, adding the North was likely to fire at areas in the Demilitarized Zone where transmitters are stationed. ‘
https://www.rt.com/news/313141-north-korea-submarines-artillery/