North Korea on Sunday warned it will carry out "a new form of nuclear test" which involves "more diversified nuclear deterrence that will be used for hitting medium- and long range targets with a variety of striking power."
The threat follows UN Security Council condemnation of the North's recent test-firing of Scud and Rodong missiles.
A government source here said U.S. intelligence agencies believe that the North's KN-08 missile has a range of up to 12,000 km, far longer than previously thought, which would allow it to reach the mainland U.S.
But it is largely thought improbable that the North has the ability to miniaturize any nuclear weapons so they could be fitted onto a missile.
A limited ballistic missile threat from North Korea and Iran to the mainland U.S. has "matured from a theoretical to a practical consideration," claimed Gen. Charles Jacoby, the commander of the North American Aerospace Defense Command, on March 13.
And National Intelligence Director James Clapper in January claimed the North is "close to deploying a new road-mobile intercontinental missile" that could threaten the mainland U.S. "We believe North Korea has already taken initial steps towards fielding this system, although it remains untested," he said.
The KN-08, which is 18 m long and 2 m in diameter, can be launched from a mobile launch vehicle.