North Korea is constructing a structure at a site where the communist country is believed to have carried out a nuclear bomb test earlier this month, military sources said Saturday.

The North announced on Oct. 9 that it had successfully performed an underground nuclear bomb test. There have been reports about signs of the reclusive regime preparing for another experiment in Punggye-ri in North Korea’s northeast.

“It is clear that there have been movements in Punggye-ri since the Oct. 9 nuclear device test,” a military source said, speaking on customary condition of anonymity.

“South Korean military and intelligence authorities are keeping tabs on the movements to check whether the North is gearing up for a second nuclear test,” he said.

However, the authorities failed to verify whether such activities are related to the North’s preparation for a second nuclear test or just camouflage, the source said.

Another military source said a second atomic test is not close at hand despite the movements in the suspected test area.

“It is certain that the North is doing something in the area, but I do not belive the North’s second nuclear test is imminent,” he said.

North Korea’s nuclear test has prompted the U.N. Security Council to adopt a resolution to impose sanctions on the country. Multilateral talks on the North’s nuclear disarmament have been stalled as Pyongyang boycotts them, citing what it calls hostile U.S. policy toward it.