North Korea has condemned the U.S. for conducting a no-explosion nuclear experiment that it claims destabilizes global security, vowing to recalibrate its own nuclear deterrence measures in response.

The U.S. Energy Department’s National Nuclear Security Administration (NNSA) announced last week that it conducted a “subcritical experiment at an underground facility in Nevada on May 14 to collect information about the reliability and effectiveness of American nuclear warheads.