JERUSALEM -- Four members of the group Hamas, including a commander of its military wing, were killed last night in an Israeli missile strike in Gaza shortly after an army official warned that "all Hamas militants are potential targets."
Some witnesses reported that two helicopter gunships fired at a group sitting under a clump of trees near the Mediterranean Sea, while others said the four men were attacked as they ran from a car with the Apaches hovering high overhead.
The strike came as Palestinian leaders said they had begun a concerted effort to rein in militant groups by closing tunnels used for smuggling and by preventing the firing of crude rockets at Israeli targets -- the first steps of what they described as a campaign to eventually seize Hamas institutions.
Israeli commanders dismissed the efforts, saying they would do nothing to prevent suicide bombings and fail to target the core members of militant groups, who must be captured or killed.
The assassinations yesterday came three days after Israel killed a member of Hamas' top political echelon -- part of a series of strikes after a suicide bomber killed 21 passengers last week aboard a bus in Jerusalem.
Israel's actions demonstrate the seriousness of statements made by its political and military leaders about eradicating militant groups such as Hamas and Islamic Jihad, as they exert tremendous pressure on the Palestinians to take action against the organizations.
Meanwhile, Israeli tanks are poised at the edge of the Gaza Strip, and officials said they will be sent in if the Palestinians do not begin a serious crackdown.
The new violence complicates efforts to restore calm and revive the U.S.-backed road map to peace. It also ends a brief weekend pause in Israeli military activity that was intended to give the Palestinian Authority a chance to arrest members of the armed factions.
"All Hamas militants are potential targets, and from our perspective, all members of the organization are part of the radical core," army Chief of Staff Moshe Yaalon told Israeli Radio yesterday. "If we see that the Palestinian Authority does not deal with this core, we will be forced to do so."
Israeli officials said they would continue military operations while expecting Palestinian security forces to work to dismantle the militant groups. Palestinian officials said the Israeli attacks cripple their police and make their work impossible.
"This obstructs our efforts and will put up new obstacles," Palestinian Minister of Information Nabil Amr said in an interview last night. "The Israelis are allowing the situation to deteriorate more than ever before."
The missile strike occurred about 9:45 p.m. in the Rimal neighborhood of Gaza City, a few hundred yards from Palestinian security chief Mohammed Dahlan's office.
Israeli military sources said the target was Ahmed Shtewe, 24, a senior member of Hamas' armed wing, the Izzedine al-Qassam Brigades. They said he was in charge of coordinating efforts in Gaza and the West Bank. Hamas said in a statement that Shtewe was the architect behind the firing of crude missiles at Israeli targets.
Also killed was Walid Hamas, another member of Hamas' military wing and head of the student association at Gaza's Islamic University. Hamas identified the other two men as Ahmad Helal and Mohammed Abu Lubda.
Israeli army officials said Helal and Lubda were suspected of being potential suicide bombers, and that intelligence indicated they were meeting Shtewe and Hamas to receive bomb belts for suicide attacks.
Witnesses said the helicopters fired missiles near a crowded section of the beach, injuring at least eight bystanders, including a child. Later, hundreds of people jammed the emergency room at Shifa Hospital, where the remains were identified, and shouted for revenge.
In an interview with the Reuters news agency minutes before the missile strike, Hamas leader Abdel Aziz Rantisi said Israeli Prime Minister Ariel Sharon had "made a big mistake" by launching a campaign of assassinations.
"He thought we were weak," Rantisi said. "Believe me, we can go ahead in this conflict forever."
Rantisi, who survived an Israeli attempt to kill him in June, rejected new attempts by the Palestinian Authority to negotiate another cease-fire and said Palestinian police would never be able to disarm his organization.
The renewed violence puts Palestinian Prime Minister Mahmoud Abbas in a precarious situation, caught between pressure from Israel and U.S. supporters to crack down on militant groups while fighting internal battles to retain control.
Arafat, whom U.S. officials are trying to isolate, has made it difficult for Abbas by preventing the prime minister from consolidating security forces under his command. U.S. officials publicly urged Arafat last week to relent.
Yesterday, Arafat offered the vacant post of interior minister to one of his closest allies, Nasser Yousef, and proposed putting him in charge of some of the police forces. That would leave Dahlan -- the security chief who has strong backing from the White House -- with little authority, and security would be firmly back in Arafat's hands.
The crisis lasted throughout yesterday and was left unresolved last night, with some officials urging Abbas and Dahlan to resign in protest. Abbas told Israeli television that neither he nor Dahlan would resign but that he would support Yousef only if all the security services are consolidated under one command.
Some Palestinian officials said last night that it would be difficult for Abbas to survive politically if this new round of violence escalates, as he would be viewed as impotent -- unable to deliver either the better life he promised the Palestinians or the security he promised Israel.
That could have a devastating effect on the peace plan. But a top Palestinian security official called the dispute between Abbas and Arafat minor, and he blamed Israel for ruining the peace process.
"Someone in Israel seems to be unhappy to see the Palestinian Authority doing its job," the official said on condition of anonymity. "Just as we were about to put all of our security under one command, they go and do something like this."
The official said there is little hope left for the resurrection of the peace process. "What else can we do?" he said. "It's extremely bad. I am very disappointed and depressed."
Earlier yesterday, it appeared Israeli commanders were at least partly pleased with Dahlan's efforts. The army's chief of staff told Israeli Radio that the Saturday raids in Gaza were the first real sign of progress.
"This might stabilize the situation, but the target is to dismantle the terrorist infrastructure," Yaalon had said. Other army commanders said they had delayed moving tanks into northern Gaza because Dahlan had started to move on the militant groups.
However, Israeli Defense Minister Shaul Mofaz later accused the Palestinians of making only cursory moves against Hamas to reduce pressure from U.S. officials and to avoid a military offensive by Israel. He said the efforts were too little, too late.
Yesterday, Palestinian militants fired a new and improved Kassam rocket, this time aimed at the Israeli coastal city of Ashkelon, about six miles from the northern border of the Gaza Strip. The missile landed on a beach near a lifeguard station less than a mile from the city, but caused no injuries.
Hamas has fired hundreds of such rockets over the past several months, most making it barely a mile outside Gaza and falling on the Israeli border town of Sederot. The missile fired at Ashkelon penetrated further into Israel than any others have and puts a new city at risk.