South Korea's Yonhap news agency said the missile had been sent by train to the newly completed missile facility of Dongchang-ni, about 40 miles (60 kilometers) from the Chinese border.
Yonhap, quoting government sources, said the missile could be ready to launch in a week or two. South Korean media have speculated that the North wants to time the launch for around June 16, when South Korean President Lee Myung-bak has a summit in Washington with President Barack Obama.
With the launch, Pyongyang could also thumb its nose at UN Security Council attempts to rein it in after last week's nuclear test and a series of short-range missile launches.
US Defense Secretary Robert Gates, speaking at a news conference in the Philippines, said North Korea appears to be working on a long-range missile but it's not clear yet what they plan to do with it.
Lee, hosting a conference of Southeast Asian leaders on the southern island of Jeju, warned the North against any provocation.
“If North Korea turns its back on dialogue and peace and dares to carry out military threats and provocations, the Republic of Korea will never tolerate that,” Lee said in his regular radio address. “I want to make clear that there won't be any compromise on things that threaten our nation's security.”