Tens of thousands of Palestinians have marched through Gaza for the funeral of Abdel Aziz al-Rantissi, the day after he was killed in an Israeli air strike.
Hamas has vowed a "volcano of revenge" against Israel
Crowds, including armed fighters from Palestinian militant groups, shouted for revenge as they threw flowers at Rantissi's shrouded body.
Hamas says a new leader in Gaza has been appointed but his identity is being kept secret for security reasons.
The killing has led to outcry from world leaders, but no US condemnation.
The White House National Security
Adviser Condoleezza Rice said on Sunday that the US had no
"advance knowledge" of Israel's operation against Rantissi.
Her comments followed suggestions in the Arab world that the US had given its blessing to Israel's action.
Hamas has vowed a "volcano of revenge" against Israel for the deaths, saying in a statement "revenge will come a hundredfold for the blood of Rantissi and Yassin".
The BBC's Peter Greste in Gaza City says Hamas claimed no Israeli is secure, but they made similar threats when Israel killed former leader Sheikh Ahmed Yassin on 22 March.
Israeli security services believe they have effectively managed to block any counter strike, but others believe Hamas is biding its time to organise a large-scale attack, our correspondent says.
Speaking from the scene of the funeral, Hamas spokesman Mahmud al-Zahar told a reporter from the BBC's World Today programme that, despite the "dark times" facing the Palestinian people, Hamas was ready to continue its policy of violent resistance.
He warned that Hamas would avenge the killing "at the proper time and proper place" saying that "without resistance occupation will be an eternal issue here".
Sea of people
The streets of Gaza ground to a halt as the cortege began its journey from the hospital where Rantissi died of his wounds on Saturday after an Israeli helicopter fired rockets at his car.
Rantissi's body - draped in a green Hamas flag - was carried shoulder-high to his home in the northern al-Nasr suburb.
After his family paid its last respects, his body was then taken to the city's main al-Omri mosque where prayers were held. Rantissi was buried in Gaza's Martyrs' Cemetery.
There were angry protests in the West Bank too, where a young Palestinian man was shot dead during clashes with Israeli troops near the controversial security barrier being constructed by the Jewish state.
Israeli Prime Minister Ariel Sharon congratulated the army on killing Rantissi, Israel Army Radio said.
And an Israeli minister said Israel also planned to kill overall Hamas leader Khaled Mashaal as soon as the opportunity arose.
Israeli officials said Rantissi was planning a large attack on Israel to consolidate his leadership of Hamas after the killing of Sheikh Yassin.
Hamas has carried out scores of suicide bombings which have killed hundreds of Israelis in recent years.
April 2004: Gaza Hamas leader Abdel Aziz al-Rantissi killed
March 2004: Hamas founder Sheikh Ahmed Yassin killed
September 2003: Sheikh Yassin survives assassination bid
August 2003: Senior Hamas figure Ismail Abu Shanab killed
June 2003: Rantissi survives attempt to kill him
July 2002: Hamas military chief in Gaza, Salah Shahada, killed
September 1997: Botched attempt to kill Hamas political leader Khaled Mashaal
January 1996: Yahya Ayyash, Hamas bomb maker, killed
Palestinian leader Yasser Arafat "vigorously condemned" Rantissi's killing.
The US, Israel's staunchest ally, refrained from condemning the attack, saying Israel had "a right to defend itself from terrorist attacks".
But, it said, it "strongly urges Israel to consider carefully the consequences of its actions" and said it was "gravely concerned for regional peace and stability".
A spokesman for the Arab League, Hossam Zaki, said the organisation condemned the attack, describing it as "state terrorism".
The timing of Rantissi's killing is particularly sensitive.
Palestinians have reacted angrily after President Bush on Wednesday endorsed Ariel Sharon's plan to retain some Jewish settlements in the West Bank and rejected Palestinian refugees' claim of a right to return to former homes in what is now Israel.