The North Korean army said it would completely cut off roads and railways connected to South Korea and fortify areas on its side of the border starting Wednesday, state media KCNA reported.

The announcement heralds a further escalation of activity near the demarcation line between the two Koreas, something that had been rare in recent years until this year.

Despite accidents, North Korea had been installing landmines and barriers for months this year and creating wasteland along the heavily militarized border, the South Korean military said in July.

The General Staff of the Korean People's Army said in a statement carried by KCNA that this was in response to war exercises held in South Korea, which described South Korea as “the primary enemy state and constant main enemy,” as well as frequent visits by US strategic nuclear facilities in the region.

South Korea's Defense Ministry said in a statement that the United Nations Command (UNC) had been informed of the matter, but declined to provide details.

South Korea is in close communication and cooperation with the UNC regarding North Korea's announcement, the ministry added.

The US-led UNC is a multinational military power and oversees affairs in the Demilitarized Zone (DMZ) between the two Koreas, which technically remain at war.

Separately, North Korea held a session of its Supreme People's Assembly this week, state media KCNA said on Wednesday, although there was no mention of whether it has officially changed its stance on the unification of the Koreas.

Tensions on the Korean peninsula have risen this year due to a series of missile tests and Pyongyang's efforts to change its relationship with the South.

There was widespread expectation that the new parliament would remove references to “unification” between the two Koreas from the constitution, in line with comments in a speech by leader Kim Jong Un in January.

KCNA also made no mention of a change in the law to designate South Korea as a “main enemy” or similar language, or a clarification of its borders amid continued strained relations between the neighbors.