Practice Relating to Nuclear Weapons
Israel’s Manual on the Rules of Warfare (2006) states:
A nuclear weapon … is a weapon like any other and is therefore subject to the usual rules applicable to weapons. Its use against civilians is forbidden. It can be put to tactical use against military targets, although apparently it is impossible to avoid its effect beyond a military target. As for the collateral damage to the surroundings and to civilians, clearly it would be forbidden to use nuclear weapons where there is no threat to the existence of the survival of a country. 
Israel, Rules of Warfare on the Battlefield, Military Advocate-General’s Corps Command, IDF School of Military Law, Second Edition, 2006, p. 22.
The Manual on the Rules of Warfare (2006) is a second edition of the Manual on the Laws of War (1998).