)
The threat came amid reports from the United Nations that China and the United States have reached agreement on new sanctions to punish the North for its atomic weapons test last month.
The North's military said in a statement on official media that it would cut off a military hotline in the truce village of Panmunjom, which straddles the heavily fortified border with South Korea.
It also threatened "strong" additional countermeasures in response to what it called US hostility.
The armistice that ended the 1950-53 war will be "completely" nullified from March 11, when the South Korean-US exercise gets into full swing in the South, it said.
The annual Foal Eagle exercise began on March 1 and will run until April 30, involving more than 10,000 US troops along with a far greater number of South Korean personnel.
Pyongyang habitually denounces such drills as a provocative rehearsal for invasion but Seoul and Washington insist they are defensive in nature.
In the past, the North threatened to scrap the armistice at times of high tension.
Pyongyang's February 12 nuclear test, its third and most powerful, attracted strong international criticism even from ally China.
The Security Council presidency was to call a closed-door meeting for 11:00 am local time, at which US and Chinese diplomats would tell the other 13 council members of progress in their talks.
"There won't be a vote today, but it could come soon. This is a sign that a draft resolution is about to be handed out," a UN diplomat told AFP on condition of anonymity.
Details of the proposed new sanctions resolution were not immediately available.
