US President George W Bush has said he is determined to see the roadmap peace plan through, despite heightened tensions after two Israeli missile strikes on Palestinian targets in the Gaza Strip.
Rantissi was targeted by at least seven missiles
Mr Bush said he was "troubled" by an Israeli missile strike in Gaza City on a car carrying the political leader of the Palestinian militant group Hamas.
As Hamas vowed an "earthquake" of revenge for the attack on Abdel-Aziz al-Rantissi, Israel launched another missile strike on Palestinians near Jabaliya who had fired home-made rockets across the border from Gaza into Israel.
Five Palestinians were killed in the attacks and dozens more - including Mr Rantissi and his son - were injured.
Israel admitted trying to kill Mr Rantissi, who it said was behind an attack on an army base in Gaza on Sunday in which four Israeli soldiers were killed.
VIOLENCE SINCE 4 JUNE PEACE SUMMIT
10 June: Israel launches two helicopter attacks in Gaza - at least five Palestinians killed; Hamas leader Abdel-Aziz Rantissi injured
9 June: Two Palestinian militants killed trying to infiltrate Jewish settlement in Gaza
8 June: Palestinian militants attack army base in Gaza - four soldiers, three militants killed; two militants shot dead after killing soldier in Hebron; militant killed after attacking troops in Gaza
7 June: Palestinian militant killed after firing on Israeli troops in Gaza
5 June: Two Palestinian militants killed in shoot-out with Israeli police in northern West Bank
Correspondents say the violence is the most serious threat yet to the fledgling US-backed peace plan, which was endorsed by Israel and the Palestinians at a peace summit in Jordan on 4 June.
Mr Bush warned that the Israeli missile strikes could undermine efforts by the Palestinian leadership to halt attacks by militants.
"I also don't believe the attacks helped Israeli security," he said.
However, he added: "I am determined to keep the process on the road to peace."
This, he said, would require "responsible leadership" from Israel and the Palestinians.
Israeli Prime Minister Ariel Sharon said Israel would continue to "fight the heads of the extremist terrorist organisations - those who initiated, those who fund and those who send terrorists to kill Jews".
Palestinian Prime Minister Mahmoud Abbas condemned the attack on Mr Rantissi as a "crime".
Vow for revenge
Mr Rantissi, a 55-year-old paediatrician and Hamas founder, leapt out of his vehicle seconds before it was hit by several missiles fired from at least two Israeli helicopter gunships.
His bodyguard and a female bystander were killed.
Speaking from his hospital bed in Gaza, Mr Rantissi vowed to continue fighting Israel and called on all Palestinian militant groups to "kill Israeli political leaders".
Hours later, three Palestinians from the same family were killed in a missile strike near the town of Jabaliya.
The Israeli army said it was targeting militants who fired Qassam rockets at Israel.
Five rockets hit the border town of Sderot, but there were no reports of injuries.
In the West Bank, Jewish settlers stepped up their attempts to stop the army removing any more unauthorised outposts after troops dismantled about 10 sites - as demanded by the roadmap.
At an outpost near the settlement of Beit El, settlers furnished hitherto empty caravans and vowed to turn the hilltop into a proper neighbourhood.
Israel's Supreme Court granted a temporary injunction blocking the demolition of the Havat Gilad outpost, after settlers launched a legal challenge against its removal.
The Israeli Government has vowed to dismantle about five more outposts over the next few days.