North Korea blows up a railway connected to the South on Oct. 15. (Yonhap-Korea Central News Agency)

In a latest development in North Korea’s isolationist policy, new blockades were being built along inter-Korean railways running along the east and west sides of the Korean Peninsula to fortify the border areas, South Korea's Unification Ministry confirmed Friday.

Kim In-ae, vice spokesperson for the Ministry of Unification in Seoul, said in a briefing that North Korea "had already built barriers at the undermined sections of Donghae lines through additional construction projects."

Kim also said similar signs of construction have been observed near the Gyeongeui lines, saying excavation works were being underway.

Earlier this month, North Korea blew up the roads and railways of the Donghae and Gyeongeui lines connecting the two Koreas close to the Military Demarcation Line.

The ministry vice spokesperson also said Friday the government was keeping a close watch on the developments in the military cooperation between Russia and North Korea.

The comments came after Russian President Vladimir Putin's press conference at the BRICS summit in Kazan the previous day, where Putin did not deny the claims that North Korea sent troops to Russia.

“Our government has repeatedly expressed grave concerns about the increasing military and economic cooperation between Russia and North Korea,” Kim said.

“As we have said, we will be taking step-by-step measures and closely following the developments, including additional dispatches.”

The South Korean delegation led by National Intelligence Service Deputy Director Hong Jang-won is set to visit NATO headquarters in Belgium next week, where they will be briefing the North Atlantic Council -- NATO's chief decision-making body -- about North Korea's troop deployment to Russia.

On North Korea convening a standing committee of the Supreme People’s Assembly on this day, the Unification Ministry vice spokesperson said laws related to their national anthem are believed to have been adopted in a continuation of efforts to "emphasize their national identity."

North Korean leader Kim Jong-un said in January he was redefining his country’s relationship with South Korea as one of “two hostile states.”