The new "Hwasung-18" ICBM "was test fired on Thursday as the key means of strategic military force," the KCNA news agency reported.

Kim said the ICBM's development "will greatly reorganise our strategic deterrence and reinforce effectiveness of our nuclear counterattack," according to KCNA.

Seoul's military said Thursday it had detected one "medium range or longer" ballistic missile launched on a lofted trajectory -- up not out -- from the Pyongyang area at 7:23 am (1023 GMT), which flew 1,000 kilometres (620 miles).

All of Pyongyang's known intercontinental ballistic missiles are liquid-fuelled, and solid-fuel ICBMs that can be launched from land or submarines have long been at the top of Kim's wish list.

Such missiles are easier to store and transport, more stable and quicker to prepare for launch, and thus harder to detect and destroy pre-emptively.

At a military parade in Pyongyang in February, North Korea showed off a record number of nuclear and intercontinental ballistic missiles, including what analysts said was possibly a new solid-fuel ICBM.

The announcement comes days before North Korea is set to mark one of its most important political anniversaries, the Day of the Sun on April 15.

The date commemorates founding leader Kim Il Sung's birth anniversary, and has typically been celebrated with significant weapons tests or military parades.