North Korea moves missile to east coast
The movement was detected by both South Korean and US intelligence, Yonhap said, citing military and government sources.
"It appeared that the object was a Musudan mid-range missile," it quoted one South Korean official as saying.
"We are closely monitoring whether the North moved it with a view to actual launch or just as a show of force against the US," the official added.
Japan's Asahi Shimbun newspaper also carried a similar report.
The Musudan missile was first unveiled at a military parade in October 2010 and is believed to have an intended range of around 3,000 kilometres. However, it is not known to have been tested.
Yonhap cited intelligence sources as saying the North might launch the missile on April 15, the birth anniversary of founding leader Kim Il-Sung.
The South Korean Defence Ministry declined to confirm the report, but stressed that it kept a "24-hour watch" for any potential North Korean missile launches.
"We believe there is always an open possibility for a missile launch and related measures have been prepared," ministry spokesman Wi Yong-Seop told reporters without elaborating.
The United States said yesterday it was sending ground-based missile interceptors to Guam in response to North Korean threats to strike the Pacific island and other US targets.
A US territory that is home to 6,000 American military personnel, submarines and bombers, Guam lies 3,380 kilometres southeast of North Korea.
Experts say the Musudan could theoretically be pushed to such a range, but the lack of tests means it lacks any proven strike capability, even on targets closer to home.