Extract from the Hague Conventions of 1907
Chapter One: Means of injuring the enemy
Article 22.
The right of belligerents to adopt means of injuring the enemy
is not unlimited.
Article 23.
In addition to the prohibitions provided by special Conventions, it is especially forbidden
(a) To employ poison or poisoned weapons;
(b) To kill or wound treacherously individuals belonging to the hostile nation or army;
(c) To kill or wound an enemy who, having laid down his arms, or having no longer means of defence, has surrendered at discretion;
(d) To declare that no quarter will be given;
(e) To employ arms, projectiles, or material calculated to cause unnecessary suffering;
(f) To make improper use of a flag of truce, of the national flag or of the military insignia and uniform of the enemy, as well as the distinctive badges of the Geneva Convention;
(g) To destroy or seize the enemy’s property, unless such destruction or seizure be imperatively demanded by the necessities of war;
(h) To declare abolished, suspended, or inadmissible in a court of law the rights and actions of the nationals of the hostile party. A belligerent is likewise forbidden to compel the nationals of the hostile party to take part in the operations of war directed against their own country, even if they were in the belligerent’s service before the commencement of the war.
These are incorporated into the 1940 US Rules of Land Warfare, just after these passages:
