The world has gotten used to belligerent language from North Korea. Pyongyang has threatened to attack Japan, warned it might fire missiles at the United States and vowed to turn the presidential palace in Seoul into a "sea of fire." None of it has happened.

But the latest threat from Kim Jong-un's regime is notable both for its simplicity and specificity: If North Korea doesn't get what it wants – the cancellation of long-planned joint sea and land exercises by the U.S. and South Korean militaries – it will tear up the 1953 armistice that ended the Korean War.

The warning, attributed to the Supreme Command of the Korean People's Army, said the armistice will be declared "invalid" on March 11, the day the U.S.-South Korea drills are due to begin. Afterward, "war manoeuvres will enter into a full-dress stage."

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On a peninsula bristling with about one million North Korean, South Korean and U.S. soldiers – plus some 20,000 armoured vehicles and artillery pieces among them – that's not an easily dismissed threat.

North Korea declared no-fly and no-sail zones starting Wednesday off its east and west coasts, suggesting it was planning major military exercises of its own. It was not clear whether the North would continue to respect the four-kilometre-wide demilitarized zone that was established by the 1953 armistice. Pyongyang also said it will cut the emergency phone line linking the U.S. and North Korean militaries.

"This land is neither the Balkans nor Iraq and Libya," the official KCNA news agency thundered. "The army and people of [North Korea] have everything, including lighter and smaller nukes unlike what they had in the past."

Most analysts see the brinksmanship as an effort to force direct talks with the United States that would see Washington provide financial aid to the regime in exchange for promises of disarmament.

But the South Korean response – a warning that it might target the leadership in Pyongyang in response to any attack – seems unlikely to calm matters. "If North Korea goes ahead with provocations and threatens the lives and safety of South Koreans, our military will strongly and sternly retaliate against the command and its supporting forces. We want to make it clear that we have made all preparations to do that," a senior military officer told a press conference in Seoul.

Despite the threats, the U.S.-South Korea military drills are expected to proceed as scheduled.

The escalation in tension comes at a delicate moment in South Korea. President Park Geun-hye was sworn in less than two weeks ago, but she has been unable to appoint a cabinet because of an impasse in the country's parliament over Ms. Park's proposals to restructure several ministries.

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North Korea's rage appears to have been prompted by moves at the United Nations Security Council to tighten sanctions against Pyongyang in response to a nuclear test last month, its third since 2006. China – which traditionally protects Pyongyang but appears to have grown frustrated with the 30-year-old Mr. Kim – has reportedly agreed to support a package of new measures that include punishments specifically targeting the North Korean elite, such as banning the sale of sports cars, yachts and jewellery to the isolated regime.

Hans Schattle, associate professor of political science at Yonsei University in Seoul, said Pyongyang has been sending "remarkably wild" signals recently, with the regime inviting prominent Americans to visit the country one week, then making threats of all-out war the next. "On the one hand, we have the regime receiving the likes of [former basketball star] Dennis Rodman and [Google chairman] Eric Schmidt; on the other hand, they are ratcheting up the bellicose rhetoric and, by some reports, stepping up live-fire artillery drills," Prof. Schattle said in an e-mail interview. "Obviously, the prospect of further sanctions – and China's willingness to go along with further sanctions – seems to be fuelling much of this."