Related Rule
United States of America
Practice Relating to Rule 149. Responsibility for Violations of International Humanitarian Law
The US Field Manual (1958) refers to Article 51 of the 1949 Geneva Convention I, Article 52 of the 1949 Geneva Convention II, Article 131 of the 1949 Geneva Convention III and Article 148 of the 1949 Geneva Convention IV and states:
No High Contracting Party shall be allowed to absolve itself or any other High Contracting Party of any liability incurred by itself or by another High Contracting Party in respect of breaches referred to in the preceding Article [war crimes]. 
United States, Field Manual 27-10, The Law of Land Warfare, US Department of the Army, 18 July 1956, as modified by Change No. 1, 15 July 1976, § 503.
The US Air Force Pamphlet (1976), in a provision stating the obligation of States to pay compensation for violations of IHL, states:
However, as a general rule, in the absence of some cause for fault such as inadequate supervision or training, no obligation for compensation arises on the part of a state for other violations of the law of armed conflict committed by individual members outside their general area of responsibility. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 10-3.
In 1992, in its final report to Congress on the conduct of the Gulf War, the US Department of Defense referred to Article 50 of the 1949 Geneva Convention I, Article 51 of the 1949 Geneva Convention II, Article 130 of the 1949 Geneva Convention III and Article 147 of the 1949 Geneva Convention IV and stated: “In a separate article common to the four 1949 Geneva Conventions, no nation has the authority to absolve itself or any other nation party to those treaties of any liability incurred by the commission of a Grave Breach.” 
United States, Department of Defense, Final Report to Congress on the Conduct of the Persian Gulf War, Appendix O, The Role of the Law of War, 10 April 1992, ILM, Vol. 31, 1992, p. 633.
The report also noted:
On 15 October [1990], the [US] President warned Iraq of its liability for war crimes. The United States was successful in incorporating into [UN Security Council] Resolution 674 … language regarding Iraq’s accountability for its war crimes, in particular its potential liability for Grave Breaches of the [1949 Geneva Conventions], and inviting States to collect relevant information regarding Iraqi Grave Breaches and provide it to the Security Council. 
United States, Department of Defense, Final Report to Congress on the Conduct of the Persian Gulf War, Appendix O, The Role of the Law of War, 10 April 1992, ILM, Vol. 31, 1992, p. 634.
According to the Report on US Practice, it is the opinio juris of the United States that “in principle, a state is responsible for any unlawful act of its armed forces in the course of an armed conflict, but not for private acts of members of its armed forces”. 
Report on US Practice, 1997, Chapter 6.3.