North Korea says it has entered a "state of war" with South Korea.
A statement carried by state media on March 30 said, "As of now, inter-Korea relations enter a state of war and all matters between the two Koreas will be handled accordingly."
The statement attributed to the North's government bodies and institutions added, "The long-standing situation of the Korean Peninsula being neither at peace nor at war is finally over."
It also warned that any military provocation would result "in a full-scale conflict and a nuclear war."
The 1953 armistice brought an end to fighting in the Korean War, but the two Koreas have technically remained at war.
The South Korean government brushed off the North's latest statement, calling it "the continuation of provocative threats."
The Unification Ministry, which handles political ties with North Korea, said the jointly run Kaesong industrial park was operating as normal with workers and vehicles crossing the border.
"North Korea's continuing threats against South Korea such as saying it is 'entering a state of war' are never acceptable since it is harming peace and stability on the Korean Peninsula," South Korean Defense Ministry spokesman Kim Min-seok told a news briefing in Seoul on March 30.
"Our recent military exercises such as Key Resolve -- Foal Eagle and the U.S. strategic bombers' deployment on the peninsula were defensive in nature against North Korea's possible provocations."
In Washington, National Security Council spokeswoman Caitlin Hayden noted that North Korea had a "long history of bellicose rhetoric and threats and today's announcement follows that familiar pattern."
Hayden added that the United States continued to take "additional measures against the North Korean threat."
Tensions on the peninsula have been high since North Korea's third nuclear test last month, which led to the imposition of new sanctions.
On March 29, Russian Foreign Minister Sergei Lavrov warned that the situation could "spiral" into a crisis.
"We are concerned that, along with the adequate reaction of the UN Security Council and the collective reaction of the world community, there are unilateral actions being taken around North Korea that are increasing military activity," Lavrov said.
Lavrov's comments came after North Korean leader Kim Jong Un ordered rockets put on standby on March 28 for strikes on the U.S. mainland and military bases in the Pacific and South Korea.
State media said the move was in response to U.S. stealth-bomber flights over the Korean Peninsula.
North Korea has threatened to attack South Korean and U.S. targets since the beginning of March, when the two allies started military exercises.
On March 27, it warned that war "may break out at any moment."
With reporting by AFP, Reuters, and AP