A unilateral promise of a ceasefire by Israel was rejected by Hamas's military wing today, triggering another round of violence. But the battle continues over the morality and legality of Israel's air war in Gaza.

Human rights groups accuse the Israeli government of unlawful conduct with its bombardment of the homes of militants in the crowded coastal enclave. The United Nations human rights chief last Friday raised "serious doubts" over Israel's compliance with international humanitarian law in Gaza.

Israel insists its Operation Protective Edge, launched with the stated goals of halting cross-border rocket fire and dealing a blow to Hamas, is defensive and proportional. It has repeatedly hit the homes of Hamas figures in Gaza, which Israel says are actually ''command and control'' centers.

Through Sunday, 52 Palestinians were killed in attacks on homes of militants, eighteen of them minors and twelve women, according to the Israeli human rights group B'tselem, which argues that the homes aren't legitimate military targets.

''They are using the phrase command and control as a sweeping excuse to demolish civilian homes. This contravenes international law, endangers civilians, and has led to a high death toll," says Sarit Michaeli, spokeswoman for B'tselem.

Army spokesman Lt. Col. Peter Lerner denies B'tselem's allegations. "We are not targeting homes. They are operation centers. When you have a command and control room and rockets and one bedroom it's not a home. It's a military position with human shields."

Human rights groups have cited specific attacks in Gaza: a July 10 strike on the al-Haj family home in Khan Yunis in which eight people – a mother and father and six children – were killed; and a Saturday strike on the home of Gaza police chief Tayseer Batsh in which eighteen people were killed. Mr. Batsh was seriously injured.

Targeting rules

International law has strict criteria for military targeting during warfare. Article 52 of the 1977 additional protocol to the Geneva Conventions of 1949 stipulates that ''attacks shall be limited strictly to military objectives. In so far as objects are concerned, military objectives are limited to those objects which by their nature, location, purpose or use make an effective contribution to military action and whose total or partial destruction, capture or neutralization in the circumstances ruling at the time offer a definite military advantage.''

One central question in assessing the legality of Israel's strikes, asks international law specialist Yael Ronen, of the Sha'arei Mishpat Academic Center in Hod Hasharon, Israel is ''what does the army mean by command and control?''

''If it's where they keep their computers, if what your destroying is the communications system inside, than it may be targetable as military infrastructure. If all you can say is this is where a person works and makes calls, without the structure of the house providing a military function, than the house doesn't qualify as a military objective because he can make his calls in the rubble or another place and Israel doesn't gain military advantage.''

Asked for evidence that houses in Gaza are being used for command and control, Lerner, the army spokesman, declined to provide specifics, only saying "Our intelligence knows where they (militant commanders) are and what specific orders they give.''

Principle of proportionality

Even if deemed a legitimate military target, the decision to attack must also be ''proportionate'' in international law. Bill Van Esveld, local representative of Human Rights Watch, says this means the military advantage gained by destroying a home must outweigh the harm done to civilians. ''I'm concerned that some of these attacks fail the first or the second tests, and this raises concerns about an unlawful policy,'' he says.

The bombing of the al-Haj family house in Khan Yunis may have failed the second test. According to Human Rights Watch, one of the sons, Omar, had joined Hamas's military wing a few months ago. ''Assuming they were going after this guy, they've blown up an entire house and killed the mother, father, six children to get this one guy. If that's what happened, it raises concerns of a disproportionate attack," says Mr. Van Esveld.

An Israeli army spokeswoman said she could not furnish any information about why the al-Haj home was targeted.

A senior Israeli legal adviser, who asked not to be named, says the military adheres strictly to the principle of proportionality and ''undertakes constraints [on targeting] that are much more significant than the constraints of international law.'' He says adhering to proportionality in Gaza is challenging ''because of the environment, working in urban terrain and because of the modus operandi of your opponent. For Hamas, their strategy and tactics is to operate within the civilian population and use it as human shields.'' The adviser adds that in Gaza the military has very good intelligence to rely on to ensure the legality of operations.

Warnings to residents

Col. Lerner says the military takes great care to avoid harming civilians: It calls residents to warn them to evacuate targeted houses even though this gives militants a chance to escape. The calls are followed by the firing of a missile without an explosive into the roof of the home to reinforce the warning. That in turn, he says, is followed up by visual confirmation that inhabitants have left the house.

Palestinians say the warning calls are not made in some instances; in others, insufficient time is given to evacuate, they say, while not all of the targeted homes house militants, they add.

Lerner, the Israeli army spokesman, says that in the attack on the home of Batsh, the deadliest such strike so far, the police chief was a target and that ''eight terrorists were on that location in the midst of planning rocket attacks. These are legitimate targets. The additional deaths are being investigated.''

Menachem Klein, a political scientist at Bar Ilan University, takes issue with the army's insistence it is getting it right. "Army lawyers are not a hundred percent neutral or in defense of civilians, they give international law cover to operations. If you use mass force, if you make a thousand flights over Gaza, the supervision over each flight with such large numbers is problematic,'' he says.

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In the view of Amos Harel, military affairs analyst for Haaretz, the army ''does not attack without a basis.''

''They try to establish proof that it's a military target based on intelligence information. But the question is whether the information is completely precise or whether in a war situation they are more flexible about what constitutes a military target,'' he says.