Israeli helicopter gunships have fired missiles in Gaza City, killing at least four Palestinians. Officials say two of them were members of the militant Islamic group Hamas. The attack is the second such operation in Gaza against Hamas activists in the past four days.

Palestinian witnesses say that Israeli helicopters fired at least three rockets at suspected members of Hamas, near the beachfront in Gaza City late Sunday evening.

Bystanders were seen carrying the bloodied body of one man to an ambulance, as helicopters hovered over the area, firing flares that lit up the night sky. Some onlookers holding up cigarette lighters also searched the ground to gather body parts.

Among those killed are members of Ezzedine al-Qassam, the military wing of Hamas, the group responsible for the suicide bombing on a bus in Jerusalem last week that killed at least 20 people.

Shortly before the raid began, the head of the Israeli Defense Forces, Moshe Ya'alon, said that the leaders of Hamas were responsible for the attack and would not go unpunished for the bombing. He said all leaders of the organization are now "potential targets for liquidation". On Thursday, Israeli helicopters fired at a car in Gaza City killing Ismail Abu Shanab and two other Hamas members.

Following his assassination, Hamas and the Islamic Jihad - another group that has carried out many suicide bombings - announced the end of a unilateral three-month ceasefire declared by Palestinian groups in late June.

Before the latest attack in Gaza, members of the Palestinian Cabinet proposed that the Palestinian militant groups agree to a new truce on condition that Israel was also bound to the agreement.

Israeli officials immediately rejected the idea, saying that the Palestinian Cabinet must first disarm and dismantle Islamic and other militia groups.