North Korea has already blocked the inter-Korean passages under leader Kim Jong-un’s instructions, South Korea’s Joint Chiefs of Staff chief Adm. Kim Myung-soo said Thursday.

The South’s JCS chairman was responding to National Assembly questions about the announcement by the North Korean army on Wednesday that the reclusive regime planned to cut off all roads and railways leading to South Korea and build fortifications in the border areas.

“North Korea began closing off the passages to the South under the direction of Kim Jong-un in December last year. They had already been completely blocked by August,” he said.

He said there were four passages connecting the North and South: the two railways of Donghae and Gyeongui along the east and west coasts, respectively; Arrowhead Hill in Gangwon Province; and Panmunjom, or the Truce Village, in the Joint Security Area.

“Of these, the JSA is heavily armed and under the close watch of the United Nations Command. North Korea laid landmines around Arrowhead Hill in April and completed removing the Donghae and Gyeongui railways in August,” he said.

He said the JCS believes one of the reasons behind the North Korean army sharing the plans for the construction with the UN Command was to “secure legitimacy” of its actions and to support leader Kim redefining the inter-Korean relations as two hostile countries.

“Based on past patterns, we believe that the North Korean regime setting up blockades is intended to further its isolation and tighten internal controls,” he said.

The North Korean army said Wednesday it informed the US military about its plans to install fortifications in the border areas to “avoid any misunderstandings or accidental clashes.” The South Korean defense ministry confirmed the North Korean announcement, saying it was closely communicating with the UN Command about the developments.

The JCS chief said based on military intelligence, the risks of a war in the Korean Peninsula were low.

“The likelihood of North Korea starting a war is not high, based on our intelligence,” he said, adding that the South Korean military was “maintaining readiness for all possible scenarios.”

He was speaking in response to a question by Democratic Party of Korea floor leader Rep. Park Chan-dae, who cited a recent US expert opinion that viewed the risks of a war in the Korean Peninsula to be at the highest levels since the Korean War.

He said the top priorities of the South Korean military were to deter any war and secure victory in the event of a war with an “overwhelming force.” “In the meantime, we are continuing vigilance in crisis management to deter any war,” he said.

On North Korea’s trash balloons, the JCS chief said collecting them after they reach the ground was deemed to be the safest approach at this point.

“If the balloons are shot down while they are still in the air, and their contents fall from a high altitude, it could lead to greater civilian damage and other unforeseen collateral damage,” he said.

He said that the South Korean military would “maintain a calm and collected response focusing on protection of the safety of our people” as North Korea keeps up “petty and base provocations.”

He warned there would be “a decisive military action” should North Korea cause “serious damage” to the South Korean public with its balloons.