SEOUL (APP) - Satellite imagery indicates a high-level of activity at North Korea 's nuclear test site as the North seeks to keep the facility ready for a try-out at all times, a US think tank said Monday.
The US-Korea Institute at Johns Hopkins University said satellite imagery from July 7 of the North's Punggye-ri shows what appears to be supplies and/or equipment stacked next to the site's North Portal where the North conducted its fourth nuclear test in January.
A small vehicle is also present at the nearby support building and several mine ore carts may also be present southeast of the portal, suggesting the tunnel is being actively worked.
"Based on imagery alone, it is not possible to determine whether this activity is for maintenance, excavation or preparation for a fifth nuclear test ", it said on its website 38 North.
"Nevertheless, it is clear that North Korea is ensuring that the facility is in a state of readiness that would allow the conduct of future nuclear tests should the order come from Pyongyang ", it added.
Pyongyang threatened on Monday to take "physical action" after Washington and Seoul announced they would deploy a sophisticated US anti-missile defence system.
The North's military, which it said was posessed of "sufficient latest offensive strike means", said in response that it would take "more merciless and powerful successive corresponding measures" against the deployment of the Terminal High Altititude Area Defence (THAAD) in the south.