South Korea's military said the North's missile flew about 700 km before landing in the East Sea. Japan estimated the missile's maximum altitude at over 2,000 km, the highest altitude ever seen by a North Korean missile.

North Korea said Monday that the missile reached an altitude of 2,111.5 kilometers in an indication that it may be a new type of a ballistic missile under development. It flew 787 km, it added.

Schilling said the high-angle launch might have been an attempt not to provoke the US too much.

"Given speculation over the past months about the possibility of military action by the Trump administration to prevent Pyongyang from acquiring such weapons, the possible testing of ICBM subsystems in this low-key manner may be a North Korean hedge against the possibility of such action," he said.

The expert said the North's missile could be a smaller, two-stage version of its three-stage KN-08 ICBM. During last month's military parade in Pyongyang, the new missile was displayed on a mobile launcher previously used for the Musudan intermediate-range ballistic missile, Schilling said.

"If North Korea has already conducted a successful test using the engines and other components of the first two stages of the KN-08, it may be closer to an operational ICBM than had been previously estimated," Schilling said. 

"Given this test and the possible North Korean path forward, a closer look will be needed to see how much progress has been made, and what technologies the North may have demonstrated, as will a reassessment of their ICBM program in that new light," he said. (Yonhap)