Catechism of the Catholic Church §2328 — excerpt
The Church and human reason assert the permanent validity of the moral law during armed conflicts. Practices deliberately contrary to the law of nations and to its universal principles are crimes.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.