Dr Matthew Harries

The CTBT is "a remarkably effective treaty, even though it hasn't come into force", said Matthew Harries, director of proliferation and nuclear policy at the RUSI think-tank in London. The treaty's verification regime includes an International Monitoring System (IMS) - a network of observation facilities around the world that are capable of detecting the sound of a nuclear explosion or the associated seismic activity or radioactive fallout.

RUSI's Harries said the next things to watch would be whether Russia would lay further groundwork for a test, perhaps by accusing Washington of preparing one, and whether it continued to support the CTBT by maintaining its share — as the United States and China do — of the global monitoring stations that track test-related seismic activity and radiation.

RUSI's Harries said the next things to watch would be whether Russia would lay further groundwork for a test, perhaps by accusing Washington of preparing one.