A US nuclear expert says no concrete evidence exists that an underground tunnel in Gilju, North Korea, is the site of a possible nuclear test.

David Albright, chief of the US Institute for Science and International Security (ISIS), on Wednesday told Radio Free Asia that to conclude the North will conduct a test is difficult.

Though other countries fear a test based on circumstances, he said Gilju shows none of the normal signs of an imminent test including movement of nuclear weapons to a certain site and cable installation in a suspected tunnel.