Practice Relating to Rule 149. Responsibility for Violations of International Humanitarian Law
Switzerland’s Basic Military Manual (1987) provides: “Violations of the laws and customs of war, commonly called war crimes, engage … the responsibility of the State to which the authors of the violation belong.”
In 2005, in a report in response to a parliamentary postulate on private security and military companies, Switzerland’s Federal Council stated:
Nonfeasance in international law or activities running counter to international law which can be ascribed to states raises the question of their so-called state responsibility. Important rules regarding state responsibility are contained in the  “Draft Articles on Responsibility of States for Internationally Wrongful Acts” of the “International Law Commission” of the United Nations (ILC), a document reflecting international customary law.
A state can be held responsible for acts carried out by its authorities who contravene international law. Conduct running counter to international law of an individual, a group of individuals, or a corporate body which are not state bodies can also be ascribed to a state if the named actors are empowered on the basis of the laws of this state to carry out sovereign activities, or if in their activities they in fact act under the instructions or under the direction or control of this state. In addition, the conduct of an individual or group of individuals, according to international law, is considered to be an act of the state if the individual or group of individuals, in the absence or default of the official authorities actually assume sovereign functions, and conditions are such that the exercise of such sovereign functions are required (Art. 5, 8 and 9 of the ILC Draft Articles).
The consequence of this state responsibility is the obligation to provide full reparation in the form of restitution, compensation and satisfaction to the wronged state or if necessary to the international community (Part 2 of the ILC Draft Articles).
Thus the conduct of private security companies mandated by states can potentially be ascribed to a state under international law.
[footnote in original omitted; emphasis in original]
In 2010, in its Report on IHL and Current Armed Conflicts, Switzerland’s Federal Council stated that “questions of State responsibility also arise with regard to private military and security companies. In fact, the  Geneva Conventions require that the High Contracting Parties commit to respecting and ensuring respect for international humanitarian law”.
(footnotes in original omitted)