Related Rule
Sweden
Practice Relating to Rule 146. Reprisals against Protected Persons
Section E. Civilians in general
Sweden’s IHL Manual (1991), referring to Article 51(6) of the 1977 Additional Protocol I and stating that this provision “contains another rule prohibiting reprisal attacks on civilian populations and individual civilians”, states:
It may appear remarkable that not until the advent of the Additional Protocol was it possible to obtain general protection for civilians against reprisals. Protection for civilians in this respect remains inadequate, however, as long as the majority of states have not ratified the Protocol.
The [Swedish] International Humanitarian Law Committee considers that Article 51 can be of great importance in improving protection for civilian populations and civilian objects. It is of the greatest importance for the article to be applied in such a way that the intended humanitarian purpose is achieved as far as possible. 
Sweden, International Humanitarian Law in Armed Conflict, with reference to the Swedish Total Defence System, Swedish Ministry of Defence, January 1991, Section § 3.2.1.5, pp. 50 and 51.
While noting that the Swedish IHL Committee strongly discourages even this possibility in view of its manifestly inhuman effect, the manual further states:
Under Additional Protocol I, reprisals are permitted only against military personnel. A state acceding to Additional Protocol I thereby accepts a limitation of its freedom to employ reprisals. The [Swedish International Humanitarian Law] Committee believes that this involves a considerable humanitarian advance. 
Sweden, International Humanitarian Law in Armed Conflict, with reference to the Swedish Total Defence System, Swedish Ministry of Defence, January 1991, Section 3.5, p. 89.