North Korea has threatened to fire at South Korean warships if they cross a disputed western sea border, one day after the South’s navy fired warning shots to chase away two North Korean ships that briefly crossed the boundary.

In a statement released through state media, the general staff of North Korea’s Korean People’s Army called the South’s action a “reckless military provocation” meant to kill the chances for dialogue between the countries.

The KPA said that the North Korean ships repelled by the South Korean navy were unarmed and said it will directly fire without warning at South Korean warships if they intrude the sea border by “even 0.001 millimeters.”

“This reckless military provocation was evidently prompted by a premeditated sinister plot to bedevil the North-South relations and further aggravate the tension on the Korean peninsula,” the KPA said about Friday’s incident.

South Korea’s navy on Friday morning fired five rounds of warning shots to chase away a North Korean military vessel and a fishing boat that briefly crossed into South Korea-controlled waters. The South had also fired warning shots after a North Korean patrol boat moved south of the boundary in February.

Minor incidents are not unusual on the western sea border, which was drawn unilaterally by the American-led UN command at the end of the 1950-53 Korean War and which the North does not recognise. However, the Koreas have also fought three bloody naval skirmishes in the area since 1999.

South Korea’s Joint Chiefs of Staff released a statement saying that the country’s military followed proper procedures to chase away the North Korean ships and called the KPA’s claim of the response being a military provocation “ridiculous.”

Since North Korea held a rare ruling party congress earlier this month, it has been demanding the South accept its calls to resume talks after months of animosities touched off by Pyongyang’s nuclear test in January and long-range rocket launch in February. South Korea has rejected the overture, saying the North must show tangible commitment to nuclear disarmament first.