Related Rule
United States of America
Practice Relating to Rule 64. Conclusion of an Agreement to Suspend Combat with the Intention of Attacking by Surprise the Adversary Relying on It
The US Field Manual (1956) provides: “To broadcast to the enemy that an armistice has been agreed upon when such is not the case would be treacherous.” 
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, § 50.
The manual also states:
It would be an outrageous act of perfidy for either party, without warning, to resume hostilities during the period of an armistice, with or without a formal denunciation thereof, except in case of urgency and upon convincing proof of intentional and serious violation of its terms by the other party. 
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, § 493.
The manual further states: “In addition to the ‘grave breaches’ of the Geneva Conventions of 1949, the following acts are representative of violations of the law of war (‘war crimes’): … violation of surrender terms.” 
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, § 504(n).
The US Air Force Pamphlet (1976) states that “the feigning of a cease-fire” is an example of perfidy. 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 8-3(a).
The Pamphlet adds: “A false broadcast to the enemy that an armistice has been agreed upon has been widely recognized to be treacherous. [This] language … expresses the customary and conventional law in this area.” 
United States, Air Force Pamphlet 110-31, International Law – The Conduct of Armed Conflict and Air Operations, US Department of the Air Force, 1976, § 8-6(a).
The US Instructor’s Guide (1985) provides that “in addition to the grave breaches of the Geneva Conventions, the following acts are further examples of war crimes: … violating surrender terms”. 
United States, Instructor’s Guide – The Law of War, Headquarters Department of the Army, Washington, April 1985, pp. 13 and 14.