North Korea has announced it has entered a "state of war" with South Korea and will 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 on Saturday.
"The long-standing situation of the Korean peninsula being neither at peace nor at war is finally over," the statement carried by the official Korean Central News Agency said.
The two Koreas have always technically remained at war because the 1950-53 Korean War concluded with an armistice rather than a peace treaty, AFP reports.
Earlier in March, North Korea announced that it was ripping up the armistice and other bilateral peace pacts signed with Seoul in protest against South Korea-US joint military exercises, which are held yearly.
The armistice was approved by the United Nations 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".
North readies missiles
On Friday, North Korean leader Kim Jong-Un put long-range missiles on standby for possible attacks on United States bases in the mainland and Pacific, after American stealth bombers flew training missions over South Korea as part of an annual drill.
Ever since North Korea was hit with United Nations sanctions following its most recent nuclear test, there has been a new tone and America has not been slow in responding, the BBC reports.
The flight of two B2 stealth bombers from the US mainland over the Korean peninsula on Friday was an open indication of America's commitment to its South Korean ally.
North Korea has been threatening to attack the South and US military bases almost on a daily basis since the beginning of March when the drills began and has ordered its armed forces on the highest alert.
But the impoverished state has kept a joint industrial zone that is the source of hard currency where hundreds of South Korean workers and vehicles enter daily.
Few believe North Korea will risk starting a full-out war.
However, North Korea's biggest trading partner China appealed for calm, while Russian Foreign Minister Sergei Lavrov warned that he could see the situation getting out of control, spiralling down into a vicious circle.
Mass rally held
Tens of thousands of North Koreans attended a huge rally in Pyongyang in a display of support for a possible military strike against the United States.
The rally in the giant Kim Il-Sung square was attended by soldiers, veterans, workers and students. Leader Kim Jong-Un was not present.
State television said Friday's rally took place to support a decision issued by the Korean People's Army supreme command - and ratified by Mr Kim - to put the country's strategic rocket units on a war footing.
Soldiers and students chanted: "Death to US imperialists".