The United States will begin nuclear testing activities “on an equal footing with other nuclear-armed states,” a senior U.S. diplomat said on Thursday.

Howard Solomon, acting chargé d’affaires and deputy permanent representative of the U.S. mission to international organisations in Vienna, said Washington had previously raised concerns that Russia and China had not adhered to a halt on nuclear tests, according to Germany’s DPA news agency.

Solomon was referring to so-called “supercritical” nuclear test explosions, which are banned under the Comprehensive Nuclear-Test-Ban Treaty (CTBT) and involve compressing fissile material to trigger a self-sustaining nuclear chain reaction resulting in an explosion.

The CTBT, signed in 1996, prohibits all nuclear test explosions, whether for military or civilian purposes, in the atmosphere, underwater, underground or on the Earth’s surface, with the aim of curbing the development of nuclear weapons.

There was no immediate comment from Russia or China on the remarks.