Jerusalem ? Less than a month after assassinating the top Hamas official, Israeli forces Saturday killed his successor, Abdel Aziz Rantisi.

The missile strike by two Israeli helicopters into Rantisi’s white compact car as it traveled on a road near his Gaza City home appeared to make good on Israel’s vow to systematically target the Hamas leadership. Sheikh Ahmed Yassin, the quadriplegic spiritual leader of the movement, was killed in a similar helicopter raid on March 22.

Rantisi, 56, was an Egyptian-trained pediatrician who helped found Hamas in 1987. The group, made up largely of Palestinians whose families fled or were forced from their homes in the Arab-Israeli war of 1948, does not recognize the existence of Israel and wants to replace it with an Islamic state.

Hamas is the most lethal of the anti-Israel Palestinian factions and is responsible for scores of suicide bombings that have killed hundreds of Israelis in more than three years of violence.

“Israel … today struck a mastermind of terrorism, with blood on his hands,” Israeli Foreign Ministry spokesman Jonathan Peled said in a statement issued to reporters. “As long as the Palestinian Authority does not lift a finger and fight terrorism, Israel will continue to have to do so itself.”

Chief Palestinian negotiator Saeb Erekat deplored the killing.

“Nations should not act like gangsters and mafias,” Erekat said.

The 8 p.m. local time attack that killed Rantisi and two bodyguards and wounded five pedestrians came just hours after an Israeli border policeman at the Erez crossing between Israel and the Gaza Strip was killed and three other Israelis wounded in a suicide bombing claimed jointly by Hamas and Al-Aqsa Martyrs’ Brigade, a militia affiliated with Palestinian leader Yasser Arafat’s Fatah faction.

“Israel will regret this. Revenge is coming,” Ismail Haniya, a Hamas leader, told reporters at the hospital where Rantisi’s shrapnel-riddled body was taken. Medics said he died on the operating table five minutes after arriving, apparently from massive head wounds.

In Washington, White House spokesman Scott McClellan repeated the Bush administration’s view that “Israel has the right to defend itself from terrorist attacks.”

While not criticizing Israel, McClellan said, “The United States strongly urges Israel to consider carefully the consequences of its actions. And we again urge all parties to exercise maximum restraint at this time.”

A tough-talking spokesman for Hamas, who was often interviewed in Arabic- and English-language media, Rantisi was targeted by Israel last June 10, after he rejected a call by then-Palestinian Prime Minister Mahmoud Abbas to comply with the U.S.-backed road map to peace by halting attacks on Israelis.

On that occasion, an Israeli helicopter gunship fired a missile into his car, killing the driver and two passersby while wounding Rantisi and his teenage son.

The next day, a Hamas suicide bomber on a bus in Jerusalem killed 16 Israelis.

Since the killing of Yassin last month, Israel has been on high alert for further Hamas attacks.

Palestinian Legislative Council member Ziad Abu-Amr had met frequently with Rantisi and other members of the extremist Palestinian factions in efforts to broker a cease-fire.

“He was a stubborn hardliner,” Abu-Amr said Saturday. “But when the majority of his people agreed to something he followed suit. … Now it seems that there is no room for a truce or an agreement of any sort, and I assume that things are bound to get worse.”