Satellite images show what appear to be three volleyball games at a North Korean nuclear test site, according to a US monitoring group.

A commercial satellite took the pictures of the Punggye-ri site on 16 April.

38 North, a monitoring project at John Hopkins University in Maryland, says the images show little activity around the north portal, a tunnel North Korea appeared to have been preparing for another nuclear test.

Instead the group spotted what it said may be three volleyball games at different locations across the site.

38 North says the images could be a sign the site has been changed to a "stand-by" status or that North Korea has taken a tactical pause in preparations at the site as part of a deception technique.


Image: Another game is apparently under way at a command centre support area in this image. Pic: Digital Globe Inc/38 North

Information on when commercial satellites will be passing overhead is readily available online, meaning the volleyball games could be North Korea's way of signalling a change of plans.

A fourth possible volleyball net appears to have been set up in the command centre area.

Volleyball is a popular sport in North Korea and games have been spotted at the facility on a number of occasions since 2006.

Image: A third image is thought to show a game at a barracks. Pic: Digital Globe Inc/38 North

The monitoring group says the status of the test site is currently unclear but it appears to be able to conduct a nuclear test at any time if ordered by Pyongyang.

The images were taken after almost eight weeks of increased activity at the site as the secretive country stepped up its missile tests, including a failed test as recently as Sunday.

Image: No game here, but this is thought to show a net at the command centre area. Pic: Digital Globe Inc/38 North

On Thursday North Korean state media threatened the United States with a "super-mighty preemptive strike" that would hit the "US mainland and reduce them to ashes".

There has been growing concern about North Korea's nuclear capabilities, but little consensus from the rest of the world as to what action can be taken to curtail it.

Russia has denied blocking a UN Security Council condemnation of the North Korea's latest missile test, accusing the US of breaking off talks on a statement in an "abrupt manner".

N Korea warned by US Vice President

The US-drafted statement reportedly demanded that North Korea "conduct no further nuclear tests" and also halt missile launches.

Russia wanted the statement to include language stressing the need to achieve a peaceful solution "through dialogue" as earlier statements have done.

The row between the two countries comes before next week's Security Council ministerial meeting on North Korea chaired by US Secretary of State Rex Tillerson.