United States of America
Practice Relating to Rule 35. Hospital and Safety Zones and Neutralized Zones
The US Field Manual (1956) restates Article 23 of the 1949 Geneva Convention I and Articles 14–15 of the 1949 Geneva Convention IV and specifies that these agreements setting up hospital and safety zones and neutralized zones “may be concluded either by the governments concerned or by subordinate military commanders”.
The US Air Force Pamphlet (1976) states:
The Geneva Conventions of 1949 provide for protected or safety zones established by agreement between the parties to the conflict. Safety zones established under the Geneva Conventions of 1949, or by other agreement among parties to a conflict, are immune from bombardment in accordance with the terms of the agreement.
The US Air Force Commander’s Handbook (1980), in a section entitled “Neutralized and Demilitarized Zones”, provides:
By agreement, the parties to a conflict may establish certain zones where civilians, the sick and wounded, or other noncombatants may gather to be safe from attack. A party to conflict cannot establish such a zone by itself; neutralized zones need only be respected if established by agreement between the parties, either oral or written, or by parallel declarations. Such an agreement may be concluded either before or during hostilities.
United States forces need not respect such a zone unless the United States has agreed to respect it. Even in an unrecognized zone, of course, only legitimate military objectives … may be attacked.
The US Naval Handbook (1995) states: “When established by agreement between the belligerents, hospital zones and neutralized zones are immune from bombardment in accordance with the terms of the agreement concerned.”
The US Naval Handbook (2007) states: “When established by agreement between the belligerents, hospital zones and neutralized zones are immune from bombardment in accordance with the terms of the agreement concerned.”
The Handbook also states: “The  Geneva Conventions recognize the special status of the ICRC and have assigned specific tasks for it to perform, including … offering its ‘good offices’ to facilitate the establishment of hospital and safety zones.”