Each State Party undertakes never under any circumstances to: […] ‘threaten to use nuclear weapons or other nuclear explosive devices.’
• Article (1)(1)(d) prohibits threatening to use a nuclear weapon or other nuclear explosive device, regardless of whether such use would itself be a violation of international law or whether the device would be used in legitimate self-defence against foreign aggression. It is therefore broader in scope than the prohibition on threat of force in Article 2(4) of the UN Charter.
• To violate the TPNW, a threat of use must be credible in the circumstances. This means that the threat must emanate from a person or an authority in a position to either effect or direct the use of a nuclear explosive device. Typically, therefore, such a threat would be made by a senior, pertinent government official or the ruling party in a nuclear-armed state.
• The narrow wording in Article 1(1)(d) of the TPNW with the active verb ‘threaten to use’ also requires that any signalled intention by a state to use nuclear weapons be specific as to the target of possible use.
• Prohibited threats may, however, be implicit as well as explicit. A stated threat does not, therefore, have to refer to use of nuclear weapons, although it would be more likely to violate the norm in the TPNW should it do so.
• In certain circumstances of tension, a show of force by means of missile testing, an explosive test of a nuclear weapon, a military exercise involving possible use of nuclear weapons, or a nuclear strike exercise, could amount to unlawfully threatening to use nuclear weapons under the TPNW (along with other violations of the Treaty).
• Policies of nuclear ‘deterrence’ rest on willingness to use nuclear weapons. Accordingly, reflecting the severity of the danger, some experts take the view that a practice of nuclear ‘deterrence’ in and of itself constitutes an unlawful threat of use of nuclear weapons. It is the view of the Nuclear Weapons Ban Monitor that the broader concept of nuclear deterrence, where the threat to use nuclear weapons is general and not specific in nature, is not sufficient in itself to constitute threatening to use under the TPNW. Deterrence practices are, however, illegal under the prohibition on possession and stockpiling.
• The NPT does not prohibit the threat of use of nuclear weapons. Threatening to use a nuclear weapon or other nuclear explosive device is prohibited under Article 1(1)(d) of the TPNW. This is the case whether such use would itself be a violation of international law or whether the device would be used in legitimate self-defence against foreign aggression. It is therefore broader in scope than the prohibition on threat of force within Article 2(4) of the UN Charter.