No signs have been detected yet that North Korea would immediately launch a long-range rocket, South Korea's defence ministry said on Friday.
"There is no sign yet that the long-range rocket launch is immediate," Xinhua quoted defence ministry spokesman Kim Min-seok as saying.
Japanese media reported that a freight train loaded with a long-range rocket headed to North Korea's rocket base at Tongchang-ri.
Freight trains unrelated to the rocket launch can move within North Korea territory, the spokesman said.
Kim added that it would not be right to link the freight trains' movement to the preparations for the long-range rocket launch.
North Korea recently erected a 67-metre launch tower for long-range rockets, taller than the previous 50-metre pad at the rocket base in Tongchang-ri.
The country fired a three-stage Unha-3 rocket into orbit in December 2012, two months before its third nuclear test.