The nuclear crisis on the Korean Peninsula hit a crescendo Monday as South Korea's military said it had uncovered signs the rival North was preparing for a fresh missile launch — possibly of a long-range weapon — and the Defense Ministry in Seoul announced it would push for the deployment of powerful U.S. strategic assets to the country.

The flurry of activity came just hours after Washington warned Pyongyang of a "massive military response" to "any threat" to the U.S. or its Asian allies in the wake of North Korea's purported hydrogen bomb test.

The South's spy agency said there is a chance that North Korea could fire an intercontinental ballistic missile on a standard trajectory into the northern Pacific Ocean, though it did not give a time frame, the South's Yonhap news agency said.