Two prominent Palestinian groups, Hamas and Islamic Jihad, have announced the end of a self-declared cease-fire. They have also vowed to carry out revenge attacks following the Israeli army's killing of a top Hamas leader in Gaza City on Thursday.
At least two others died when Israeli helicopter gunships fired rockets at a car carrying Hamas leader Ismail Abu Shanab.
Hamas and Islamic Jihad announced in a series of phone calls to media organizations Thursday that they are canceling a unilateral three-month truce.
The cease-fire was first declared with other armed Palestinian groups in late June.
The decision followed Israel's assassination of senior Hamas leader Ismail Abu Shanab in a residential neighborhood of Gaza City.
The Israeli operation was part of a series of military actions in response to the Hamas suicide bombing in Jerusalem on Tuesday that killed at least 20 people on a commuter bus.
Israeli forces also carried out a series of incursions into West Bank cities Thursday to search for suspected Islamic militants.
The Israeli actions came despite an appeal from the Palestinian prime minister, Mahmoud Abbas, to allow the Palestinian security forces to launch their own crackdown against Hamas and the Islamic Jihad, two groups that frequently carry out suicide bombings.
Mr. Abbas condemned Thursday's killing of the Hamas leader as an ugly crime and said the Israeli operation would hinder Palestinian Authority efforts to rein in Islamic militants.
On Wednesday, the Palestinian Cabinet approved tough measures against Hamas and Islamic Jihad. The planned moves included disarming the armed wings of both organizations.
Palestinian Security Minister Mohammad Dahlan said Thursday that these plans are now on hold because of the assassination of Mr. Abu Shanab.
Earlier, the office of Israeli Prime Minister Ariel Sharon issued a strong statement in support of Israeli military operations.
The statement says there is no chance of peace efforts succeeding as long as the Palestinian Authority refuses to take action against Hamas and other Palestinian armed groups.