"Given their size and shape, the components transferred by train from an ammunition factory near Pyongyang appear to be for a three-stage rocket," Kyodo quoted sources in the Japanese secret services as saying.
The components are being transferred by train to the Tongchang-ri site in North Pyongan province, ITAR-Tass reported.
The missile, believed similar to one launched from Tongchang-ri in April 2012, may be launched by the end of the year, Japanese experts said.
"While no missile is set on a launch pad yet, there are activities likely to be related to rocket fueling," the Kyodo agency reported, citing information from a U.S. surveillance satellite.
The April launch was a failure as the Unha-3 carrier disintegrated moments after it was launched.
Resolution 1874 of the U.N. Security Council prohibits North Korea from ballistic missile activity and the April launch attempt brought international condemnation.