The Israeli military yesterday sealed off the West Bank and Gaza Strip in response to Palestinian rocket attacks.

The army said 21 rockets fired from Gaza fell in Israel yesterday, injuring five Israelis.

Israel earlier responded with airstrikes on what the army called Hamas weapons facilities. The attacks were the first airstrikes in Gaza since Israel withdrew from the coastal strip last week after 38 years of occupation.

Witnesses said two of those killed were members of the armed wing of Islamic fundamentalist group Hamas who were driving in two cars when a helicopter fired two missiles, one ploughing into each vehicle.

Hamas sources named one of the victims as 17-year-old Rwad Farhad, a member of its armed wing, the Ezzedine al-Qassam Brigades.

Doctor Mouawiya Hassanein, head of emergency services in the Gaza Strip, told AFP that four people were killed in the incident, which happened near the former Jewish settlement of Netzarim.

Two of the dead were transferred to hospital, but Hassanein said the bodies of another two victims were torn to pieces in the blast.

Palestinian interior ministry spokesman Tawiq Abu Khossa confirmed there had been an Israeli air raid, however, there was no immediate comment from the Israeli military.

Earlier an explosion at a militant Hamas rally killed at least 15 Palestinians, including children and gunmen, in the Gaza Strip on Friday in the first deadly incident in the territory since Israel completed its withdrawal.

Palestinian President Mahmoud Abbas's Fatah group and the Palestinian interior ministry said Hamas was responsible.

"The Fatah Central Committee holds the Hamas movement fully responsible for the victims of the military parade (that was held) among civilians," Fatah's Central Committee said in a statement.

Hamas said the explosion was the result of an Israeli airstrike, while Israel denied all involvement.

The explosion in the densely packed Jabalya refugee camp, which killed 15 people, including at least two children and three militants, occurred after Islamic Jihad militants fired rockets into Israel in retaliation for a deadly West Bank raid.

Senior Hamas leader Nizar Rayan, whose brother, a local commander for the group, died in the blast, said Israeli drones or helicopters targeted a vehicle carrying five Hamas gunmen.

He said that while Hamas would continue to honour an eight-month ceasefire it had agreed to in February by request of Abbas, it would still respond to Israeli attacks against Palestinians.

Fatah's Central Committee slammed Hamas for displaying munitions at the rally, which marked a show of armed force by the group following Israel's Gaza pullout on September 12 after 38 years of occupation, among thousands of civilians.

"The Fatah Central Committee calls upon all groups to stop these military parades and to put all weapons and explosives away from residential neighbourhoods," the group said.

Medics said more than 60 people were wounded in the blast, which wrecked the Hamas vehicle. But Rayan denied reports that it had carried explosives, saying the vehicle only contained plastic models of rockets that could not detonate.