Related Rule
Israel
Practice Relating to Rule 10. Civilian Objects’ Loss of Protection from Attack
Israel’s Manual on the Laws of War (1998) states:
A situation may arise where the target changes its appearance from civilian to military or vice versa. For instance, if anti-aircraft batteries are stationed on a school roof or a sniper is positioned in a mosque’s minaret, the protection imparted to the facility by its being a civilian object will be removed, and the attacking party will be allowed to hit it … A reverse situation may also occur in which an originally military objective becomes a civilian object, as for instance, a large military base that is converted to a collection point for the wounded, and is thus rendered immune to attack. 
Israel, Laws of War in the Battlefield, Manual, Military Advocate General Headquarters, Military School, 1998, p. 38.
Israel’s Manual on the Rules of Warfare (2006) states:
It may be the case that a target might change its status from civilian to military or vice versa. For example, if an anti-aircraft battery is positioned on the roof of a school or if a sniper takes up a position on the minaret of a mosque, the protection provided for the facility by the virtue of it being [a] civilian target is no longer valid, and the attacker is permitted to attack it. The legal responsibility for the deaths of civilians in such a case is that of the side that made unreasonable use of a civilian target rather than on the side who attacked this target. In the case of incidents in which there is a doubt as to whether the target changed its status from civilian to military, the Additional Protocols determine that it should be assumed that it is not a military target unless proven otherwise.
The opposite situation may occur, in which a target that was originally military changes into a civilian target, such as a large military base converted into a clearing station for the wounded. In such cases, it must not be attacked as it is a medical facility (on the assumption that no military activities are conducted therein, being disguised as treatment for the wounded). 
Israel, Rules of Warfare on the Battlefield, Military Advocate-General’s Corps Command, IDF School of Military Law, Second Edition, 2006, p. 27.
The manual further states: “Protected places (hospitals, places of worship, etc.) must remain protected as long as military action is not being deployed therefrom.” 
Israel, Rules of Warfare on the Battlefield, Military Advocate-General’s Corps Command, IDF School of Military Law, Second Edition, 2006, p. 49.
The Manual on the Rules of Warfare (2006) is a second edition of the Manual on the Laws of War (1998).
In 2009, in a report on Israeli operations in Gaza between 27 December 2008 and 18 January 2009 (the “Gaza Operation”, also known as “Operation Cast Lead”), Israel’s Ministry of Foreign Affairs stated:
The loss of absolute protection for a civilian site when it is misused by the adversary as a locus for military operations is broadly recognised in the Law of Armed Conflict. Thus, for instance, the hidden placement of a significant military asset within a civilian building or even the presence of enemy combatants can make the otherwise civilian site amenable to attack. This is a harsh reality of urban warfare. 
Israel, Ministry of Foreign Affairs, The Operation in Gaza 27 December 2008–18 January 2009: Factual and Legal Aspects, 29 July 2009, § 107.
[footnotes in original omitted]
The report further stated;
110. … [A] commander’s intent is critical in reviewing the principle of distinction during armed conflict. Where it is believed in good faith, on the basis of the best available intelligence, that a civilian building has been misused as a sanctuary for military fighters, military intelligence, or the storage and manufacture of military assets, the commander has a legitimate basis for using force against the site. This is so even where judgment is based on limited information in a fluid battlefield situation.
111. The definition of military targets thus could include terrorists who move rapidly throughout a neighbourhood, even where they shelter themselves in civilian dwellings. It does not relieve the commander of the obligation to judge the proportionality of his action. But it makes clear that a civilian site can be converted to a legitimate target by the conduct of the opposing force in using such places for military purposes, including the escape of armed combatants. 
Israel, Ministry of Foreign Affairs, The Operation in Gaza 27 December 2008–18 January 2009: Factual and Legal Aspects, 29 July 2009, §§ 110–111.
The report also stated: “When a civilian objective is used by the enemy for a military activity it loses its protection and immunity and becomes a legitimate military target. Nevertheless, when striking such a target, special care shall be taken to adhere to the principle of proportionality.” 
Israel, Ministry of Foreign Affairs, The Operation in Gaza 27 December 2008–18 January 2009: Factual and Legal Aspects, 29 July 2009, § 223.
The report added: “In accordance with the Law of Armed Conflict, civilian facilities that served military purposes did not enjoy protection from attack. Thus, a residential building that doubled as an ammunition depot or military headquarters was a legitimate military target for attack.” 
Israel, Ministry of Foreign Affairs, The Operation in Gaza 27 December 2008–18 January 2009: Factual and Legal Aspects, 29 July 2009, § 233.
Israel’s Manual on the Laws of War (1998) states: “In cases where there is doubt as to whether a civilian object has turned into a military objective, the [1977] Additional Protocols state that one is to assume that it is not a military objective unless proven otherwise.” 
Israel, Laws of War in the Battlefield, Manual, Military Advocate General Headquarters, Military School, 1998, p. 38.
Israel’s Manual on the Rules of Warfare (2006) states:
In the case of incidents in which there is a doubt as to whether the target changed its status from civilian to military, the Additional Protocols determine that it should be assumed that it is not a military target unless proven otherwise. 
Israel, Rules of Warfare on the Battlefield, Military Advocate-General’s Corps Command, IDF School of Military Law, Second Edition, 2006, p. 27.
The Manual on the Rules of Warfare (2006) is a second edition of the Manual on the Laws of War (1998).
The Report on the Practice of Israel states:
In principle, in cases of significant doubt as to whether a target is legitimate or civilian, the decision would be to refrain from attacking the target. It should be stressed that the introduction of the adjective “significant” in this context is aimed at excluding those cases in which there exists a slight possibility that the definition of the target as legitimate is mistaken. In such cases, the decision whether or not to attack rests with the commander in the field, who has to decide whether or not the possibility of mistake is significant enough to warrant not launching the attack. 
Report on the Practice of Israel, 1997, Chapter 1.3.
In 2009, in a report on Israeli operations in Gaza between 27 December 2008 and 18 January 2009 (the “Gaza Operation”, also known as “Operation Cast Lead”), Israel’s Ministry of Foreign Affairs stated:
A dual use objective may be attacked if reliable, conclusive and up-to-date information confirms that it serves the military activities of the enemy, and subject to the principle of proportionality. In case of doubt, such objective shall be presumed to be civilian. 
Israel, Ministry of Foreign Affairs, The Operation in Gaza 27 December 2008–18 January 2009: Factual and Legal Aspects, 29 July 2009, § 223.