Mexico
Practice Relating to Nuclear Weapons
In 1996, during a debate in the First Committee of the UN General Assembly, Mexico stated:
Mexico therefore expresses its full support for the initiative taken by Brazil concerning the recognition that the various Treaties establishing nuclear-weapon-free zones are gradually freeing the southern hemisphere and adjacent areas of nuclear weapons. We need to develop mechanisms of cooperation among the various zones as part of the efforts to consolidate the respective regimes. While negotiations on these Treaties have responded to the characteristics of each region, they have also largely taken into account the experience of those areas where similar regimes already existed.
Mexico had argued before the Court the existence of rules of international law that leave no doubt about the illegality of the threat or use of nuclear weapons in any circumstance. 
Mexico, Statement before the First Committee of the UN General Assembly, UN Doc. A/C.1/51/PV.3, 14 October 1996, pp. 6–7.
In 1996, during a debate in the First Committee of the UN General Assembly, Mexico stated:
The illegality of the use of [nuclear] weapons was the subject of the Court’s Advisory Opinion. However, we believe that a legally binding instrument would be an important step in a phased programme towards the complete elimination of nuclear weapons within a time-bound framework. 
Mexico, Statement before the First Committee of the UN General Assembly, UN Doc. A/C.1/51/PV.18, 11 November 1996, p. 12.
In 2009, Mexico submitted a proposal to the UN Secretary General to amend Article 8(2)(c) of the 1998 ICC Statute in accordance with Article 121(1) of the Statute, stating:
[T]he Mexican Delegation wishes to reassert its amendment proposal to article 8 of the Rome Statute to criminalize the use or threat of use of nuclear weapons as a war crime [in international armed conflict].
Criminalizing the use of weapons of mass destruction – including nuclear weapons – is not a new issue for States Parties to the ICC Statute. Deliberations over this topic were not concluded when the ICC Statute was adopted, despite efforts displayed by Mexico and other like-minded delegations. Consistent with Mexico’s advocacy for the total prohibition of nuclear weapons, the Mexican delegation confirms its conviction of criminalizing the use of nuclear weapons as a war crime.
Proposed amendment
Add to article 8, paragraph 2, b), the following:
(...) Employing nuclear weapons or threatening to employ nuclear weapons. 
Mexico, Proposal of Amendment to Article 8(2)(c) of the 1998 ICC Statute, submitted to the UN Secretary General in accordance with Article 121(1) of the ICC Statute, 29 September 2009, p. 2.
[emphasis in original]
In 2009, during the assembly of the States Parties to the 1998 ICC Statute, the representative of Mexico stated:
I would like to briefly refer to my country’s proposal to include the use of nuclear weapons and the threat to use nuclear weapons as war crimes in the Rome Statute. … [F]or Mexico, the use of nuclear weapons and the threat to use nuclear weapons are prohibited under international law. The unnecessary damage and suffering which a nuclear explosion would cause during an armed conflict clearly justifies its absolute prohibition and classification as a war crime. 
Mexico, Statement by the representative of Mexico during the 8th session of the Assembly of the States Parties to the Rome Statute of the International Criminal Court, The Hague, 19 November 2009.
In 2010, during the general debate of the Review Conference of the 1998 ICC Statute, the Undersecretary for Foreign Affairs of Mexico stated: “[W]e are convinced that the [1998] Rome Statute will not be complete until the use of nuclear weapons is included as a war crime.” 
Mexico, Statement by the Undersecretary for Foreign Affairs of Mexico during the general debate of the Review Conference of the Rome Statute of the International Criminal Court, Kampala, 31 May 2010, p. 1.
In 2010, during a debate in the UN General Assembly on the Report of the International Criminal Court, the legal adviser of the Ministry of Foreign Affairs stated:
I would like to reiterate my country’s belief that the [1998] Rome Statute will not be complete until the use of nuclear weapons is classified as a war crime. We will therefore continue to promote that cause in the working group to be established by the Assembly of States Parties during its next session. 
Mexico, Statement by the legal adviser of the Ministry of Foreign Affairs before the 65th session of the UN General Assembly, UN Doc A/65/PV.39, 28 October 2010, p. 24.