North Korea said it was ending its commitment to the armistice that halted the Korean War in the 1950s after the U.N. Security Council passed sanctions in response to a February nuclear test.
U.S. State Department spokeswoman Victoria Nuland said "trash-talking" from Pyongyang will only lead to further isolation for the North Korean regime.
Pyongyang in December orbited a satellite using a long-range rocket. Similar launches in 2006 and 2009 coincided with the country's first two nuclear tests.
Blog 38 North from Johns Hopkins notes that satellite imagery gathered from January through early March show "no signs" that North Korea is preparing to fire another rocket at either of its two test facilities.
There was some activity at the Tonghae launch site in the north of the country but researchers said evidence wasn't solid enough to reach any conclusions.
"If Pyongyang adheres to the same timetable followed in the past, a new launch campaign will last a little over nine weeks," the researchers said.