Related Rule
United States of America
Practice Relating to Rule 32. Humanitarian Relief Objects
The US Field Manual (1956) notes that, in case of occupation, if the occupied territory is inadequately supplied, “all Contracting Parties shall permit the free passage of [relief] consignments and shall guarantee their protection”. 
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, § 388.
In 1992, in a report submitted pursuant to paragraph 5 of Security Council Resolution 771 (1992) on grave breaches of the 1949 Geneva Convention IV committed in the former Yugoslavia, the United States included among “deliberate attacks on non-combatants” reports that “a convoy of United Nations trucks carrying aid supplies to Bosnian civilians was mortared” and that a “G-222 aircraft, which was carrying five tons of blankets to Sarajevo on a United Nations relief mission, was shot down by up to three ground-to-air missiles”. 
United States, Former Yugoslavia: Grave Breaches of the Fourth Geneva Convention, annexed to Letter dated 22 September 1992 to the UN Secretary-General, UN Doc. S/24583, 23 September 1992, p. 8.
In another such report, the United States referred to a report that “an International Committee of the Red Cross (ICRC) convoy carrying food and medical relief on 18 May was attacked as it entered Sarajevo, despite the security guarantees obtained from the parties concerned”. 
United States, Former Yugoslavia: Grave Breaches of the Fourth Geneva Convention (Third Submission), annexed to Letter dated 5 November 1992 to the UN Secretary-General, UN Doc. S/24791, 10 November, p. 19.
According to the Report on US Practice, it is the opinio juris of the United States that “buildings used for relief and other charitable purposes are not subject to bombardment”. 
Report on US Practice, 1997, Chapter 4.2.