"North Korea blew up sections of Gyeonggi and Donghae roads north of the military demarcation line around noon," the Joint Chiefs of Staff of the South Korean Armed Forces said in a statement.
The military said it had increased surveillance and readiness to respond.
Last week, the General Staff of the Korean People's Army warned that from October 9 it would block all roads and railways connected to South Korea, reports interfax.ru.
"The acute military situation on the Korean peninsula requires our army to take more decisive and powerful measures to further reliably protect the security of the state," the North Korean General Staff said in a statement released by KCNA.
"For our army, the constant closure and blockade of the southern border with the ROK (Republic of Korea), the main hostile state and the constant main enemy, in the current situation is a measure of self-defense to prevent war and protect the security of the DPRK," Pyongyang stressed.
