From Responding to Hamas Attacks from Gaza – Issues of Proportionality:
Israel is forced to act in self-defense to protect itself from deliberate missile attacks on its civilians by Hamas terrorists. Although Hamas makes no effort to comply with international law, Israel is committed to limiting itself to a lawful response. This means that, while Hamas uses civilians both as a shield and a target, Israel seeks to limit injury to civilians on both sides.
International law recognizes that for a military operation to be lawful, it must be directed at a “legitimate military objective” and be “proportionate.”
Under the Geneva Conventions, if a military objective, such as a missile launcher or weapons stockpile, is placed in the heart of a civilian area, it does not cease being a lawful military objective. The responsibility for civilian casualties arising from the “shielding” lies with the party that deliberately placed civilians at risk.
A survey of international practice suggests that the steps taken by Israel, and its approach to proportionality, correspond to, or are more stringent than, those taken by most Western countries confronting similar threats.