Related Rule
United States of America
Practice Relating to Rule 111. Protection of the Wounded, Sick and Shipwrecked against Pillage and Ill-Treatment
The US Field Manual (1956) states that the parties shall take all possible measures to protect the wounded and sick against pillage and ill-treatment and prevent their being despoiled. 
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, § 216.
The US Air Force Pamphlet (1976) refers to Article 15 of the 1949 Geneva Convention I and states the obligation to protect the sick and wounded from pillage and ill-treatment. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 12-3(a).
The US Naval Handbook (1995) provides that “mistreating enemy forces, the shipwrecked disabled by sickness or wounds” is a war crime. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-2.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Transportation, US Coast Guard, October 1995 (formerly NWP 9 (Rev. A)/FMFM 1-10, October 1989), § 6.2.5.
The US Naval Handbook (2007) states that examples of war crimes that could be considered as grave breaches of the 1949 Geneva Conventions include:
3. Offenses against the sick and wounded, including … mistreating enemy forces disabled by sickness or wounds.
5. Offenses against the survivors of ships … lost at sea, including … mistreating the shipwrecked. 
United States, The Commander’s Handbook on the Law of Naval Operations, NWP 1-14M/MCWP 5-12.1/COMDTPUB P5800.7, issued by the Department of the Navy, Office of the Chief of Naval Operations and Headquarters, US Marine Corps, and Department of Homeland Security, US Coast Guard, July 2007, § 6.2.6(6); see also § 6.2.6(3) and (5).
The US Manual on Detainee Operations (2008) states:
Legal Considerations
a. As a subset of military operations, detainee operations must comply with the law of war during all armed conflicts, however such conflicts are characterized, and in all other military operations …
c. The four Geneva Conventions of 1949 are fully applicable as a matter of international law to all military operations that qualify as international armed conflicts … The principles reflected in these treaties are considered customary international law, binding on all nations during international armed conflict. Although often referred to collectively as the “Geneva Conventions,” the specific treaties are:
(1) [1949] Geneva Convention [I] … This convention provides protection for members of the armed forces and other persons on the battlefield who are no longer actively participating in hostilities as the result of becoming wounded or sick. It also regulates the conduct and treatment of medical and medical support personnel. It requires humane treatment for wounded and sick personnel who fall into enemy hands, with an express requirement that such individuals be … protected against pillage and ill treatment. 
United States, Manual on Detainee Operations, Joint Chiefs of Staff, 30 May 2008, pp. I-2–I-3.
According to the Report on US Practice, it is the opinio juris of the United States that the wounded and sick in internal armed conflicts should be respected and protected in accordance with Article 8 of the 1977 Additional Protocol II. 
Report on US Practice, 1997, Chapter 5.1.
The US Field Manual (1956) provides: “The civilian population shall respect [the] wounded and sick, and in particular abstain from offering them violence.” 
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, § 219.
The US Health Service Manual (1991) reproduces Article 18 of the 1949 Geneva Convention I and provides: “The civilian population must respect the wounded and the sick and refrain from offering them violence.” 
United States, Field Manual 8–10, Health Service Support in a Theatre of Operations, Department of the Army Headquarters, 1 March 1991, p. A-2.