A published report says the United States, Japan and South Korea are closely monitoring a North Korean missile base where brisk activity has been observed.
South Korea's Chosun Ilbo reports North Korea has relocated mobile missile launchers at the Jeongju base, north of Pyongyang, in recent days.
The newspaper quotes a South Korean government official as saying it is not clear whether the activity is part of preparations for missile tests, or part of routine training.
South Korea's Defense Ministry has refused to confirm the report, and Japan says it is not aware of any missile base movements.
The report comes amid renewed efforts to restart six-way talks on North Korea's nuclear ambitions.