Israeli tanks and bulldozers attacked a Palestinian security post in a Gaza refugee camp Saturday, and three Palestinians were killed in a gunbattle. In the West Bank, an explosion from a car killed a Hamas militant.

The Israeli army said Palestinians in the Gaza Strip fired a Qassam-2-type rocket into Israel, the second such attack from Gaza. It prompted sharp warnings from the military, which considers the weapons an escalation.

Israel has said it will retaliate strongly for use of the rocket, which was developed by the Islamic militant group Hamas and has a range of three to five miles, longer than mortars used in the past.

The rocket landed in an open field in Kfar Azza, and no one was injured, the army said.

"This is a serious aggravation, we cannot support such a threat and in spite of our warnings we have another rocket fired," said Olivier Rafowicz, an army spokesman.

Nazih Abu Sabaa, a leading member of Hamas' military wing, was killed Saturday when a car near him exploded in the West Bank town of Jenin, Palestinian security officials said. The car was wired with explosives, they said.

Palestinian security officials blamed Israel for his death. The Israeli army had no immediate comment.

Witnesses said Abu Sabaa had left the nearby school where he teaches and was walking near a vegetable market in Jenin when a car parked nearby exploded. A 2-year-old boy standing nearby was lightly injured in the blast.

Thousands of Palestinians gathered at the scene, many chanting "revenge, revenge."

"The Zionist enemy should know very clearly that all the crimes including this assassination will not pass without a strong reaction," said Mahmoud Zahar, a Hamas spokesman.

Hamas and another radical group, Islamic Jihad, have been responsible for scores of suicide bombing attacks that have killed dozens of Israelis.

Israel has killed dozens of suspected Palestinian militants in targeted attacks during the past 16 months of fighting. Several bystanders have also been killed in these attacks. Israel says it has to take action because the Palestinian Authority is not doing enough to prevent attacks.

Palestinian militants on Friday attacked a checkpoint north of Ramallah in the West Bank, killing an Israeli, Israeli security sources said.

Meanwhile, Israeli troops launched a number of operations in the Gaza Strip on Saturday, days after the military was shaken by a Palestinian bomb attack that destroyed an Israeli Merkava-3 tank and killed three soldiers.

Israeli tanks, military vehicles and bulldozers attacked a Palestinian security compound Saturday in the el-Bourrej refugee camp south of Gaza City. Israel said the incursion was in response to Palestinians shooting over the fence into Israel, and that forces set up a checkpoint in the area to maintain control.

Clashes erupted between Israeli troops and Palestinian security forces and gunmen. Palestinians from the camp also joined in, throwing stones and petrol bombs, witnesses said.

During heavy exchanges of fire, three Palestinians were killed and 13 injured, Palestinian security and hospital officials said.

"This policy of killing Palestinians will not get us anywhere," said Palestinian Cabinet Minister Nabil Shaath.

Earlier Saturday, Israeli tanks and troops entered a Gaza City neighborhood and fired at a Palestinian security compound. The army said they were training facilities, Palestinian security sources said the building belonged to Palestinian intelligence.

Israeli troops also stormed several houses and arrested people in central Gaza, near the Jewish settlement of Netzarim, the area where Palestinian militants planted a 110-pound bomb that destroyed the Israeli tank on Thursday. Bulldozers cleared vegetation and agricultural lands in the area, Israeli army and Palestinian security sources said

The bombing of the tank marked the first time Palestinians destroyed a major piece of Israeli military hardware. The Merkava is one of the most heavily armored tanks in the world.

After 16 months of fighting with relatively few casualties, the deaths startled the military. On Friday the commander of an elite undercover unit, Col. Eyal Weiss, 34, was killed when a wall collapsed during the demolition of the home of a suspected Islamic militant by army bulldozers.

German Foreign Minister Joschka Fischer met with Palestinian leader Yasser Arafat on Saturday and called for a return to negotiations.

"Terror and violence must come to an end, what we need is an opening of the door to negotiations and opening the door to peace between the two people, Israel and Palestine," Fischer said.

The Palestinian Cabinet condemned the latest Israeli military action, saying it would "only lead to more violence, lack of security and more anger."