It was a notable sharpening in the North's often bellicose rhetoric and followed word from U.N. diplomats that the United States and China had struck a tentative deal on a draft U.N. Security Council sanctions resolution that would punish North Korea for its third nuclear test, which it conducted last month.
"We will completely nullify the Korean armistice," the North's KCNA news agency said, quoting the Korean People's Army (KPA) Supreme Command spokesman.
"The war exercise being done by the United States and the puppet south Korea is a systematic act of destruction aimed at the Korean armistice."
The two Koreas remain technically at war since the 1950-53 conflict ended in a truce rather than a peace treaty.
"We will be suspending the activities of the KPA representative office at Panmunjom (truce village) that had been tentatively operated by our army as the negotiating body to establish a peace regime on the Korean peninsula," KCNA quoted the spokesman as saying.
"Related to that, we will be making the decision in parallel to cut off the Panmunjom DPRK-U.S. military hotline.
North Korea, officially called the Democratic People's Republic of Korea (DPRK), has made much of hotlines with the South and the United States over the years, but has not been known ever to have used them in times of increased tension.
About 200,000 Korean troops and 10,000 U.S. forces are expected to be mobilized for their defensive "Foal Eagle" exercise, under the Combined Forces Command, which began on March 1 and goes on until the end of April. Separate computer-simulated drills called "Key Resolve" start on March 11.
Speaking on condition of anonymity, the U.N. diplomats said they hoped to receive the draft resolution on North Korea at Tuesday's council session. They added that they would like to see the council vote on the resolution by the end of this week.
"I hope to see a draft tomorrow perhaps, but you know it's up to the Americans," a diplomat told Reuters on condition of anonymity. Details of the draft were not immediately available.
The U.N. press office announced separately that Russia, which holds the presidency of the 15-nation Security Council this month, would convene closed-door consultations on North Korea at 11 a.m. EST (1600 GMT) in New York on Tuesday.
China asks for prudent response
China's Foreign Ministry declined to confirm that it had reached a deal with the United States.
"We have said many times that China supports an appropriate response from the U.N. Security Council and have also expressed our stance that we oppose North Korea conducting its nuclear test," spokeswoman Hua Chunying told reporters.
"At the same time, we are resolute in believing that the relevant response has to be prudent and moderate, has to prevent an escalation, be conducive to the denuclearization of the Korean peninsula, prevent nuclear proliferation and maintain the peace and stability of Northeast Asia."
Council diplomats have said that they would like to strengthen the provisions in previous sanctions resolutions adopted after North Korea's 2006 and 2009 nuclear tests - above all those related to the inspection and seizure of shipments of banned items and toughening financial restrictions.
The U.N. Security Council strongly condemned North Korea's third nuclear test, on February 12, and vowed to take action against Pyongyang for an act denounced by all major world powers, including ally China.
Pyongyang said at the time that the test was an act of self-defense against "U.S. hostility" and threatened stronger steps if necessary.
In January the Security Council passed a resolution expanding U.N. sanctions against North Korea due to its December rocket launch and warned Pyongyang against further launches or nuclear tests. North Korea responded by threatening a new atomic detonation, which it then carried out the following month.
North Korea's previous nuclear tests prompted the Security Council to impose sanctions that included a ban on the import of nuclear and missile technology, an arms embargo and a ban on luxury goods imports.
There are 17 North Korean entities, including banks and trading companies, on the U.N. blacklist, and nine individuals - all linked to North Korea's nuclear and missile programs. U.N. diplomats say many more entities and individuals could be subject to international asset freezes and travel bans.
Beijing has supported all previous sanctions resolutions against Pyongyang but only after working hard to dilute proposed measures in negotiations on the texts. It has been concerned that tougher sanctions could further weaken the North's economy and prompt refugees to flood into China.