North Korea announced on Saturday that it was in a state of war with South Korea, in its ongoing angry rhetoric against South Korea and the US.
In a statement carried by the official Korean Central News Agency (KCNA), Pyongyang said all inter-Korean issues would be dealt with in a wartime manner.
The two Koreas have technically remained at war after a ceasefire — and not a peace treaty — ended the 1950-53 Korean War.
The military was waiting for further orders from leader Kim Jong Un, KCNA reported.
On Friday, Kim issued orders to prepare strategic missiles for attack on the US and South Korea.
Pyongyang was reacting to a show of force by US stealth fighters that flew a 20,000-km round trip to drop dummy bombs onto a South Korean training ground.
Despite the latest threat, North Korea was still allowing commuters through its border, the Defence Ministry in Seoul said.
Relations have deteriorated since North Korea’s third nuclear test on February 12, which led to a strengthening of international sanctions against it.
It has since issued repeated threats, including pre-emptive nuclear attacks.
Hundreds of South Koreans travel across the border to the jointly run Kaesong industrial complex daily, except Sundays. The park is one of the only sources of foreign currency for impoverished, isolated North Korea.