While the Trump administration attempts to play hardball with the North Korean regime, workers at the country’s nuclear testing site appear happy to indulge in a more leisurely pursuit: a game of volleyball.

Satellite images taken of the Punggye-ri site in the country’s mountainous north-east at the weekend showed little human activity to suggest North Korea was preparing to conduct a nuclear test.

But four of the images carried on the 38 North website, a monitoring project based in Washington, showed teams of people playing volleyball – a popular sport among North Koreans – not far from where the regime has conducted all of its underground nuclear detonations.

“We see that at three locations in the facility – in the main administrative area, at the support area, at the command centre and at the guard barracks near the command centre – they have volleyball games going on,” said Joe Bermudez, an expert at 38 North.

The images could mean the site is in the midst of an athletic interlude as final preparations are made for a nuclear test. Or, given that North Korean authorities know when commercial satellites are flying overhead, it could have been an act of mischief intended to confuse the outside world.

“It suggests that the facility might be going into a standby mode,” Bermudez said. “It also suggests that these volleyball games are being conducted with the North Koreans knowing that we will be looking and reporting on it. They are either sending us a message that they have put the facility on standby, or they are trying to deceive us.”

Bermudez said the images showed evidence of tunneling work, but there was no sign that water had been pumped out of the tunnel system where the nuclear tests take place.

Speculation that North Korea would conduct its sixth nuclear test in just over a decade to coincide with last Saturday’s celebrations marking the birth of the country’s founder, Kim Il-sung, proved unfounded.

Instead, the regime test-fired a missile the following day that the US said had exploded seconds after its launch.

North 38 said satellites had sent back images of personnel playing volleyball at the Punggye-ri site on several occasions stretching back to 2006, the year North Korea conducted its first nuclear test.