North Korea is taking measures to "permanently shut down and block the southern border" to South Korea, announces the country's military. Roads and railways that have facilitated travel between the two countries are being closed, according to the announcement.
The closure is described by North Korea as a "great military step".
North Korea has previously closed its reunification agency and declared South Korea as the country's main enemy.
The US military has been informed of the decision to avoid "misjudgments and unintentional conflict", announces North Korea.
