SEOUL-- South Korea and the United States are closely watching the possibility of North Korea resuming provocative acts, the South's military said Tuesday, following a report about signs of potential missile test in the North.

Japan's Kyodo News reported that the Japanese government is on alert after radio signals suggested that North Korea might be preparing for a ballistic missile launch.

It added that, as satellite images have not shown a missile or a movable launch pad, the signs may also be related to its winter military training.

"The South Korean military is closely monitoring and tracking possible North Korean provocations in collaboration with the U.S.," said Army Col. Roh Jae-cheon, spokesman of the Joints Chiefs of Staff.

North Korea has refrained from provocations for about 70 days since its launch of an intermediate-range ballistic missile over Japan on Sept. 15.

A government source said that in recent weeks, signs of brisk activity have been detected at North Korean missile bases.

"More monitoring is needed to gauge whether the North is trying to launch a missile or is preparing for winter training that starts in December," the source said.

A day ago, the North appeared to have operated a radar which tracks a missile's trajectory, and signs were detected that the use of communication devices had increased in the North's missile bases, it added.

The militaries of Seoul, Washington and Tokyo are sharing related information and keeping close tabs on the North's activity, it added.

Source: Yonhap News Agency