North Korea has announced that it has entered a "state of war" with South Korea and would deal with every inter-Korean issue accordingly.
"As of now, inter-Korea relations enter a state of war and all matters between the two Koreas will be handled according to wartime protocol," the North said in a joint statement attributed to all government bodies and institutions.
"The long-standing situation of the Korean peninsula being neither at peace nor at war is finally over."
The statement was carried by the official Korean Central News Agency (KCNA).
The North threatened on Saturday to shut down a joint industrial complex with South Korea, state news agency KCNA reported, in the latest warning from Pyongyang at a time of escalated tensions between the two sides.
The threat from the state body in charge of the complex just north of the Korean border followed an announcement by the North on Wednesday that it was cutting its last military hotline with the South.
But an official from the South said the joint industrial complex, which lies inside North Korea, was operating normally on Sunday despite the North's threat.
Technically at war
The two Koreas have always technically remained at war because the 1950-53 Korean War concluded with an armistice rather than a peace treaty.
South Korea's Unification Ministry quickly released a statement calling the latest threat not new and saying it is a follow-up to Kim's earlier order to put troops on a high alert in response to annual US-South Korean defence drills.
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North Korea sees those drills as rehearsals for an invasion.
On Friday, North Korean leader Kim Jong-un warned his forces were ready "to settle accounts with the US" after two American B-2 bombers flew a training mission in South Korea.
The White House said it took a new warning from North Korea that it was in a state of war with South Korea seriously, but said Pyongyang's threats were following a familiar pattern.
"We've seen reports of a new and unconstructive statement from North Korea. We take these threats seriously and remain in close contact with our South Korean allies," said Caitlin Hayden, spokeswoman for the National Security
Resumption of hostilities
The North had announced earlier this month that it was tearing up the armistice and other bilateral peace pacts signed with the South in protest against South Korea-US joint military exercises.
Voiding the ceasefire theoretically opened the way to a resumption of hostilities, although observers noted it was far from the first time that North Korea had announced the demise of the armistice.
The armistice was approved by the UN General Assembly, and both the UN and South Korea have repudiated the North's unilateral withdrawal.
Saturday's statement also warned that any military provocation near the North-South land or sea border would result "in a full-scale conflict and a nuclear war".