At least two Palestinian militants have been killed in an Israeli air strike in the Gaza Strip, as violence escalates less than two weeks after the Israeli pullout.

Israeli aircraft fired missiles at two cars carrying gunmen from the Islamic militant group Hamas in Gaza City. The vehicles exploded in flames. It was the latest of several air strikes in Gaza on Saturday, in retaliation for Hamas rocket attacks on Israeli towns.

Earlier, the air force targeted Hamas weapons factories and rocket launching sites. Israeli ground forces and artillery units are massing on the Gaza border, and the West Bank has been sealed off.

The Palestinian Authority called the air strikes "a criminal act of aggression." Israel said, now that it has ended its 38-year occupation of Gaza, it will respond to Palestinian attacks with a crushing blow.

"No doubt that any kind of attack against the sovereign state of Israel requires us to take very harsh measures to make certain that these attacks are stopped, and not repeated," said government spokesman Ra'anan Gissin.

Militants fired rockets after at least 15 Palestinians were killed in an explosion on Friday. The blast occurred as gunmen displayed weapons during a military parade at a Gaza refugee camp. Hamas blamed Israel, but the Palestinian Authority said the blast was caused by militants who mishandled explosives.

Palestinian chief negotiator Saeb Erekat told VOA that Hamas should stop parading weapons, and abide by the seven-month-old cease-fire.

"Seeking revenge or violence will only add to the complexities and will harm Palestinian interests," Mr. Erekat noted.

Israeli officials issued a strong warning to the Palestinian Authority: if it does not take action to rein in militants, Israel will.