Satellite imagery of North Korea’s nuclear test site shows activity that could indicate preparation for a nuclear weapons test, according to Johns Hopkins University’s U.S.-Korea Institute in Washington.

A report Friday from 38 North, a Web project of the institute devoted to analysis of North Korean developments, said the site appeared capable of conducting a nuclear test at any time the order was received from Pyongyang. Pictures of the test site, it said, showed new activity near the site’s north portal.

The images were thought to show at least five mining carts, one small equipment trailer and a net canopy that could be concealing equipment beneath it. 38 North said the pumping of water used to maintain a stable environment for the nuclear materials seemed to have ceased.

Also, images of the Main Administrative Area showed a small truck or van present in a courtyard, along with “several unidentified objects and activities.” Analysts said they might be supplies or equipment concealed by tarps.

The analysts responsible for the report, Joseph Bermudez and Jack Liu, said it was unclear whether the new signs indicated a “tactical pause” preceding a nuclear test, or a broader and longer “stand-down” from normal facility operations.

North Korea has conducted five nuclear weapons tests since 2006, including two last year.