South Korea military officials who spoke anonymously to local news services EDaily and the Kukmin Ilbo said North Korea has yet to perfect the technology that could allow for the atmospheric re-entry of a long-range ballistic missile.
The reports come a week after a Japanese television network reported North Korea placed two new intercontinental ballistic missiles into position in an area north of Pyongyang.
But officials in Seoul are now saying North Korea has not developed any new ICBMs aside from the KN-08 and the KN-14.
North Korea is likely to test-launch a midrange Musudan because the missile needs technical improvements, and its detonator and atmospheric re-entry need to be tested.
During his New Year's speech, Kim said North Korea had reached the final stage of preparations for launching an ICBM, and state media said a launch could take place at "any time, any place" in the weeks that followed.
Last week, state-controlled television network KCTV aired footage of past launches of the Musudan. The footage included the partly successful launch of the midrange missile that took place in June 2016.
Pyongyang has test-launched a total of eight Musudan missiles, but most of the tests ended in failure, according to EDaily.
The missile has a range of 1,900 to 2,500 miles and is capable of targeting Japan and the U.S. military base in Guam.
Experts say North Korea's ICBMs, the KN-08 and the relatively new KN-14, are combining two Musudan engines as a single-stage propulsion system, Kukmin Ilbo reported.