Related Rule
Spain
Practice Relating to Rule 106. Conditions for Prisoner-of-War Status
Section B. Levée en masse
Spain’s LOAC Manual (1996) considers the population of a territory that spontaneously takes up arms against an invading army to be combatants, provided they are part of an organized force, commanded by a person responsible for the conduct of his or her subordinates, subject to an internal disciplinary system, and comply with the law of war. 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Publicación OR7-004, 2 Tomos, aprobado por el Estado Mayor del Ejército, Division de Operaciones, 18 March 1996, Vol. I, § 1.3.a.(1).
Spain’s LOAC Manual (2007) states that “inhabitants of a territory who spontaneously take up arms to resist invading forces” are lawful combatants. [Such inhabitants] “must also fulfil the following collective requirements to be considered lawful combatants”:
- organized forces;
- under a command responsible for the conduct of its subordinates;
- internal disciplinary system;
- compliance with the law of armed conflict. 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Tomo 1, Publicación OR7–004, (Edición Segunda), Mando de Adiestramiento y Doctrina, Dirección de Doctrina, Orgánica y Materiales, 2 November 2007, § 1.3.a.(1).
The manual further states: “The civilian population has the right to spontaneously take up arms to resist the invading forces, provided that they carry arms openly and respect the law of armed conflict.” 
Spain, Orientaciones. El Derecho de los Conflictos Armados, Tomo 1, Publicación OR7–004, (Edición Segunda), Mando de Adiestramiento y Doctrina, Dirección de Doctrina, Orgánica y Materiales, 2 November 2007, § 2.7.a.(1).