Kerry said a missile test would be provocation that would further isolate the country and its impoverished people.

NPR: NKorea, Marking Leader's Birthday, Shows More Ire

Also Monday, President Lee and leaders at a summit of the Association of Southeast Asian Nations called the test a "provocation" that threatens world peace, according to news reports.

WSJ: Pyongyang at Work On Missile, U.S. Says

Panetta said a nuclear test would be considered a provocation and "worsen our relationship, " though he refused to discuss specific action the United States would take in response.

CNN: Panetta: 'We're within an inch of war almost every day'

Secretary of State John Kerry warned North Korea not to conduct a missile test, saying it will be an act of provocation that "will raise people's temperatures" and further isolate the country and its people.

NPR: A Look At The North Korea Crisis