An Israeli missile attack on a car in Gaza has killed four members of the Islamic militant group Hamas, including one of the organisation's military leaders and founders.
Israel has intensified operations against Hamas in Gaza
Hundreds of angry Hamas supporters have gathered at the Gaza City hospital where Ibrahim al-Maqadma's body was taken.
The helicopter attack came hours after two Israelis were shot dead by Palestinians who infiltrated the settlement of Kiryat Arba, near Hebron in the West Bank.
The military wing of the Palestinian militant group Hamas claimed responsibility for the settlement raid late on Friday.
The two gunmen were shot dead by troops.
All Israeli leaders will be open targets for Hamas
Abdel-Aziz al-Rantissi, Hamas official
Eight other people, including a number of soldiers, were also wounded in the attack.
The upsurge in violence comes as the PLO's decision-making council is due to debate the creation of a new post of prime minister for the Palestinian Authority.
Palestinian leader Yasser Arafat has nominated his deputy in the PLO, Mahmoud Abbas, for the post. Mr Abbas has not yet accepted.
Witnesses said two Israeli helicopters fired on the militants' car, which was reduced to a charred wreckage.
"One fired, then the other fired. They fired at least four missiles," Gaza resident Hana Abu Musa said.
Several people were reported to have been injured in the attack, one of them in critical condition, Palestinian hospital officials said.
The helicopter attack also left several people injured
After the Gaza missile attack, Israeli helicopters remained overhead, causing schoolchildren to leave their classes and rush home.
It was the latest of a number of Israeli strikes against Hamas in Gaza, where for the past three weeks the Israeli army has been conducting a major operation to crush the militants.
Last week, Israeli forces captured a co-founder of the Hamas movement, Mohammed Taha, during a raid on Gaza, in which several civilians were killed.
Confirming the death of one its military leaders on Saturday, Hamas vowed revenge.
"The assassination of Ibrahim al-Maqadma will launch a new stage of war against the Jews," senior Hamas official Abdel-Aziz al-Rantissi told Reuters news agency.
"All Israeli leaders will be open targets for Hamas," he said.
In recent days, Qassam rockets have been launched from Gaza across the boundary into Israel.
Two Israelis were killed when gunmen infiltrated a settlement
Three of the home-made rockets slammed into the town of Sderot on Thursday - there were no casualties.
Early on Friday, Israeli troops reoccupied part of the northern Gaza Strip, in an operation to stop such attacks.
An army spokesman said the operation - in which dozens of Palestinians are reported to have been wounded - was open-ended.
Scores of people have been killed over the past few days in Israel and the Palestinian territories.
Friday's attack on the Kiryat Arba settlement occurred after the beginning of the Jewish Sabbath.
According to eyewitnesses, the gunmen slipped into the settlement disguised as Jewish seminary students.
After the gunmen entered a family home and opened fire, troops rushed to the scene and exchanged fire before the two Palestinians were killed.
In a second attempted attack on Friday night, Israeli troops shot dead two Palestinians trying to infiltrate the nearby settlement of Negohot, military sources said.
The Gaza Strip was also the scene of violence during the day.
Israeli troops shot dead three Palestinians near the Jewish settlement of Netzarim, south of Gaza City.
Israeli military sources said the men had opened fire on a convoy of Jewish settlers - but Palestinians sources said they were farmers not gunmen.