The missile isn’t capable of hitting the US mainland, Bloomberg cited South Korean Defense Minister Kim Kwan Jin as telling lawmakers.
The move is being interpreted as the latest in a string of provocations by Pyongyang.
The Yonhap news agency quoted an unnamed South Korean official who said they were "closely monitoring whether the North moved it with a view to actual launch or just as a show of force against the US."
North Korea on Thursday morning local time issued another threat against US, saying that that its military has been cleared to wage an attack on the US using "smaller, lighter and diversified nuclear" weapons.
Deutsche Welle cited a statement by North Korea's official KCNA news agency on Thursday as saying the general staff of the Korea People's Army had "ratified" a nuclear attack on the US.
In response to that move, US Defense Department spokesperson Lt. Col. Cathy Wilkinson told GlobalPost:
"We've seen today's statement by North Korea, again making unhelpful and unconstructive threats. It is yet another offering in a long line of provocative statements that only serve to further isolate North Korea from the rest of the international community and undermine its goal of economic development. North Korea should stop its provocative threats and instead concentrate on abiding by its international obligations."
The US announced shortly before North Korea's statement that it is moving an advanced missile defense system to Guam, in the Pacific, in the next several weeks — two years ahead of schedule.
US Defense Secretary Chuck Hagel has warned that North Korea is a "real and clear danger" to the US and its allies.
Japan's Asahi newspaper, meanwhile, reported that a US intelligence satellite spotted what appeared to be a long-range KN-08 missile being transported on a train in North Korea to the Sea of Japan coast.
The missile being moved was said to be a Musudan-type medium range missile.
The Musudan, also known as the BM-25, is a medium-range ground-launched missile that could be fitted with a nuclear warhead, although analysts doubt the North could do that.