The Qana tragedy has intensified accusations that Israel’s actions in Lebanon violate international law. Every death of an innocent person is extremely regrettable; but there is no evidence Israel has committed any war crimes. In contrast, Hezbollah, Iran and Syria have clearly violated international law in this conflict. Moreover, Israel’s conduct compares favorably to how its most powerful accusers have behaved when their own interests have been threatened.

International law has three major prohibitions relevant to the Qana incident. One forbids deliberate attacks on civilians. Another prohibits hiding forces in civilian areas, thereby turning civilians into "human shields." A third prohibition, the proportionality restriction that Israel is accused of violating, involves a complicated and controversial balancing test.

Geneva Convention Protocol I contains one version of the proportionality test, the International Criminal Court Statute another; neither is universally accepted. As a result, the proportionality test is governed by "customary international law," an amalgam of non-universal treaty law, court decisions, and how influential nations actually behave. It does not hinge on the relative number of casualties, or the force used, however, but on the intent of the combatant. Under customary international law, proportionality prohibits attacks expected to cause incidental death or injury to civilians if this harm would, on balance, be excessive in relation to the overall legitimate military accomplishment anticipated.

At Qana, Israeli aircraft fired toward a building to stop Hezbollah from shooting rockets at its cities. The aircraft did not deliberately target civilians; but Hezbollah rockets are targeted at civilians, a clear war crime. U.N. humanitarian chief Jan Egeland last week called on Hezbollah to stop its "cowardly blending" among women and children: "I heard they were proud because they lost very few fighters and that it was the civilians bearing the brunt of this." If Hezbollah used Lebanese civilians in Qana as "human shields," then Hezbollah, not Israel, is legally responsible for their deaths.

If Israel was mistaken and Hezbollah was not firing from or hiding amongst these civilians, the legality of its action is assessed by the proportionality test. Because the test is vague, there have been few, if any, cases since World War II in which a soldier, commander or country has been convicted of violating it. In the absence of guidance from the courts, determining whether Israel’s military has failed the proportionality test depends on an assessment of what civilian casualties it expected, what its overall military goals are, the context in which the country is operating, and how the international community has in practice balanced civilian risk against military goals.

Israel did not expect civilian casualties; it warned civilians to leave Qana, and Israel’s official investigation has concluded its military attacked based on "information that the building was not inhabited by civilians and was being used as a hiding place for terrorists." The law of war recognizes that mistakes are inevitable, and does not criminalize soldiers who seek in good faith seek to avoid them.

Israel’s overall military goal is to survive attacks by enemies determined to annihilate it. Hezbollah leader Hassan Nasrallah has stated: "Israel…is an aggressive, illegal and illegitimate entity, which has no future…Its destiny is manifested in our motto: ‘Death to Israel.’" Thus Israel is attempting to prevent Hezbollah from using its 10,000 remaining rockets, and to implement the requirement of U.N. Security Council Resolution 1559 that Hezbollah be disarmed.

Meanwhile, Hezbollah and Iran — which provides this terrorist group with arms, direction and over $100 million a year — are in continual violation of international law. Their calls for Israel’s destruction violate the international genocide treaty’s prohibition of "direct and public incitement to commit genocide." Iran’s effort to develop a nuclear arsenal that could obliterate Israel, or deter its responses to future Hezbollah attacks, violates the Nuclear Nonproliferation Treaty. Iranian (and Syrian) support for Hezbollah violates U.N. Security Council Resolution 1373, requiring states to "refrain from providing any form of support, active or passive, to entities or persons involved in terrorist acts." Hezbollah began the armed conflict with rocket attacks on Israeli towns and the abduction of Israeli soldiers: unprovoked acts of war violating an internationally recognized border.

Israel is acting in self-defense and avoided killing civilians, even giving advance notice by phone to the occupants of homes targeted for attack as Hezbollah hideouts. While Hezbollah deliberately maximizes harm to Israeli and Lebanese civilians, Israel puts its soldiers at risk to minimize Lebanese civilian casualties.

The track record of many of Israel’s most powerful accusers — including China, Russia and the European Union — is not nearly as good at balancing civilian risk against military goals.

China killed hundreds of peaceful Tiananmen Square protestors in 1989. It has for five decades occupied Tibet, slaughtering tens of thousands; and it vows to invade Taiwan if it declares independence. Neither the Tiananmen protesters nor Tibet nor Taiwan has ever threatened to "wipe China off the map."

Russia has fought since 1994 to suppress Chechnya’s independence movement. Out of a Chechen population of one million, as many as 200,000 have been killed as Russia has leveled the capital city of Grozny. Chechen rebels pose no threat to "wipe Russia off the map." All of the leading EU countries actively participated in NATO’s 78-day bombing campaign against Yugoslavia in 1999. The military goal was to stop Yugoslavia from oppressing its Kosovar minority. NATO bombs and missiles hit Yugoslav bridges, power plants and a television station, killing hundreds of civilians. Yugoslavia posed no threat to the existence of any of the EU countries that bombed it.

Compared with how China, Russia, and the EU have dealt with non-existential threats — and despite the law-flouting behavior of Hezbollah, Iran and Syria — Israel’s responses to the threats to its existence have been remarkably restrained rather than disproportionately violent.

Mr. Kittrie is professor of international law at Arizona State University and served in the Office of the Legal Adviser at the U.S. State Department from 1993 to 2003.