WASHINGTON -- Satellite imagery shows little activity at North Korea's nuclear test site, though one of its tunnels is ready for the communist nation's sixth nuclear test at any time, the monitoring website 38 North said Wednesday.

Commercial satellite imagery on April 16 of the Punggye-ri test site showed what may be three volleyball games underway at different locations throughout the facility, but little activity was shown at the North Portal, where test preparations had been under way.

One of the possible explanations for the decreased activity may be that the "site and associated preparations for a sixth nuclear test have transitioned to a 'stand-by' status, with personnel being allowed some down-time for recreation," 38 North said.

"Since the North Koreans are aware of when commercial satellites will fly overhead, the presence of personnel at play (with what looks like the normal six players on each side) may be a way of signaling that a decision has been made to place the test on hold," it said.

Still, however, satellite imagery continues to indicate that the Punggye-ri site appears able to conduct a sixth nuclear test at any time once the order is received from Pyongyang, 38 North said. (Yonhap)