Al-Rantisi had become Hamas' top official only recently -- after the assassination of the group's spiritual leader, Ahmad Yassin, in an Israeli missile attack on 22 March.
Hundreds of thousands of Palestinians vowed vengeance in protests across Gaza and the West Bank yesterday. Militants shouted: "The blood of Yassin and al-Rantisi will not be wasted. Their blood will force the eruption of new volcanoes."
A top Hamas official, Mahmud al-Zahar, said at al-Rantisi's funeral, "We are ready, we are sure that Israel will fail to suppress the resistance regime. We are going to continue our armed struggle."
Al-Rantisi's killing was denounced by European nations and Japan as unhelpful to peace efforts and unlawful.
But underscoring the growing chasm between Washington and much of the rest of the world on the Israeli-Palestinian crisis, the U.S. declined to condemn the act and defended what it called Israel's right of self-defense -- though it denied it had any prior knowledge of the attack.
The killing occurred just days after U.S. President George W. Bush came out in favor of a controversial plan by Israel to pull out of Gaza but retain key settlements on the West Bank -- a plan many of Washington's European allies said would harm prospects for peace.
Analysts and political leaders say Washington's stance on al-Rantisi's killing and backing of Israel's plan are likely to have a negative impact on Middle East peace -- at least in the short-term -- as well as on U.S. efforts to win over Arab hearts and minds, particularly in Iraq.
But there are signs as well that Washington may be becoming increasingly concerned about its image in the Arab world. Republican Senator John Warner of Virginia said yesterday that he feels al-Rantisi's killing harms U.S. interests.
"The timing of this assassination concerns me because, just as you saw pictures earlier of literally tens of thousands of people in the Palestinian areas expressing their remorse, expressing their anger, that same picture is on every television camera, every television set in Iraq," Warner said.
Meanwhile, by endorsing Israeli Prime Minister Ariel Sharon's plan to leave Gaza but hold on to key Jewish settlements in the West Bank, Bush appeared to affect a sea change in U.S. policy toward the Middle East.
Analysts say that's because Bush did two things that no U.S. president has ever done: he said Israel cannot be expected to give up all land captured in the 1967 Middle East war, and he rejected the right of Palestinian refugees to return to Israel.
Both of those points have long been considered as up for negotiation between Israel and Palestinians during final status talks. But Daniel Neep, director of Middle East studies at London's Royal United Services Institute, tells RFE/RL that Bush's words have had the effect of appearing to impose final conditions on the Palestinians, without their having a say in the matter.
"For a U.S. president to say that, basically takes away cards that a Palestinian negotiating team would have in their hands, and really does to a considerable extent prejudice the outcome of those final status negotiations. So I think we're moving away from allowing the sides to talk to each other, to imposing a kind of settlement on them," Neep said.
In a letter to world leaders yesterday, Qurie accused the United States of breaking international law by making "concessions" in the name of the Palestinians. He also urged the international community to restart Middle East peace talks.
The so-called "Quartet" comprised of the United States, Russia, the European Union, and the United Nations is expected to discuss the situation early next month.
Sharon's plan must still be approved by the Likud Party.
Analysts say the EU's reaction to Bush's support for the plan has been pragmatic, motivated by a desire not to further exacerbate tensions with Washington.
A spokeswoman for Javier Solana, the EU foreign policy chief, echoed that approach. Christina Gallach tells RFE/RL's correspondent in Brussels that the EU believes Israel's withdrawal from Gaza could be positive -- if carried out under certain conditions.
For now, both EU leaders and some U.S. officials emphasize that regardless of the Israeli plan, it will still be up to Israel and the Palestinians to work out any final settlement between them.
However, Palestinians are facing a growing problem of leadership, says Neep, which is only likely to worsen after al-Rantisi's assassination. He says the popularity of Hamas is growing at the expense of Yassir Arafat's Palestinian Authority, essentially leaving the Palestinian people without a truly credible interlocutor in any future talks with Israel.
"Even if the Palestinian Authority were to re-engage in negotiations, there's no real legitimacy for them to do so coming from the Palestinian people. The Palestinian public [is] so disillusioned and dissatisfied with the entire peace process and everything surrounding it, that even if an agreement were to be reached it simply wouldn't stick, I think. I think it wouldn't have the backing of any of the grassroots movements or the wider public at all," Neep said.