Israel's assassination earlier this month of Hamas chief Abdel Aziz Rantisi stirred gusts of indignation from European governments. As in previous cases, the critics largely rested their case on international law, a refrain also heard often from the continent's critics of American counterterror measures and of the war in Iraq.

British Foreign Minister Jack Straw asserted that "targeted killings of this kind are unlawful [and] unjustified." The French foreign ministry issued a statement saying that Israel's right to self-defense "should not be exercised against international law." The foreign minister of Ireland, which currently holds the presidency of the European Union, declared that "extrajudicial killings are contrary to international laws." Swedish Prime Minister Goran Persson called Israel's action "illegal and disgusting." Spokesmen for the governments of Germany, Italy, Austria, Portugal, and Russia made similar comments.

If the law is what these Europeans say it is, then, as Dickens's Mr. Bumble put it, "the law is a ass" because the moral case for Israel's counterattacks on Hamas is overwhelming. But even in strictly legal terms, Israel's actions have sound justification. Ironically and shamefully, it is not Israel but these very critics of Israel who are in flagrant dereliction of their legal obligations...

Each of these European states is a party to the Convention on the Prevention and Punishment of Genocide. Unlike, say, the Universal Declaration of Human Rights, the genocide convention is a treaty, with the force of law. It is one of the oldest, and perhaps the most widely subscribed piece of international human-rights legislation, and arguably the one with the soundest legal foundation, codifying what the Nuremberg tribunal and the U.N. General Assembly in its very first session found to be existing customary law.

Article One of the convention obligates every party "to prevent and punish" genocide as "a crime under international law." The convention goes on to define genocide as, inter alia, "killing" intended "to destroy, in whole or in part, a national, ethnical, racial or religious group."

By this definition, it is clear that Hamas is an organization devoted to genocide and has been working busily at this mission for years. Hamas's goal is the complete destruction of the Jewish state. As the late Rantisi himself affirmed: "By God, we will not leave one Jew in Palestine." Nor did Rantisi leave doubt about what would become of these Jews. Asked by an interviewer "what do you see ultimately happening to the people [of] Israel?" Rantisi replied: "They killed thousands of Palestinians.... so I think it is just to do with them as they did with us."

Nor are Hamas's intended targets limited to Israeli Jews. Hamas's covenant boasts: "HAMAS regards itself the spearhead and the vanguard of the circle of struggle against World Zionism [and] the fight against the warmongering Jews." It makes clear that there is to be no end of killing: "The Day of Judgment will not come about until Muslims fight the Jews and kill them. Then, the Jews will hide behind rocks and trees, and the rocks and trees will cry out: 'O Muslim, there is a Jew hiding behind me, come and kill him.'"

In short, Hamas's and Rantisi's platform is as clearly formulated a project of genocide as we have had since Mein Kampf. And indeed, Hamas has expressed a solicitousness for Hitler's project. As Rantisi put it, to compare Zionism to Nazism is "an insult to Nazism."

Nor can this all be dismissed as mere rhetoric. Hamas sends a constant stream of bombers to blow up buses, restaurants, markets, any place, in short, where Jews can be slaughtered. For every one whose murderous deed is achieved, handfuls of others are stopped along the way by Israeli security.

What this means is that France, Sweden, and the rest are under a legal obligation to do what they can to destroy or cripple Hamas and to assist in the arrest and prosecution of its leaders and members. What have they done to fulfill this responsibility?

Until six months ago, the EU allowed Hamas to work freely in Europe, as if it were just another NGO. The rationale was a specious distinction between the organization's "political" and "military" wings, much like the distinction between Hitler's Nazi party and his storm troopers. (Indeed, this distinction was drawn, leading the Times of London to applaud the "night of long knives" on the grounds that Hitler was bringing the "radicals" in his movement to heel.)

Only late last year were French objections overcome in the face of a particularly deadly bombing, and Hamas was banned in the EU, its financial assets frozen. But under the genocide convention, Europe's legal obligations (and those of all the other parties to the treaty) go well beyond belatedly closing its own territory to Hamas operations. They include doing what can be done to bring a halt to the genocide and punish the perpetrators. By killing the likes of Rantisi and Yassin, Israel is doing what all the other nations ought by law to be doing, too. Since they are blithely indifferent to their own solemn undertakings, Israel is left alone to defend the law and itself.

— Joshua Muravchik, a resident scholar at the American Enterprise Institute, is author of Heaven on Earth: The Rise and Fall of Socialism and, most recently of, The Intifada and the Media